Ronald Clark O’Bryan was convicted of the murder of his own child in a Texas state court in 1974 and sentenced to die. On appeal from the federal district court’s denial of habeas corpus relief, 28 U.S.C. § 2254 (1976), the defendant contends:
(1) that the exclusion of three jurors who expressed conscientious objections to the death penalty violated the rule of *369Witherspoon v. Illinois, 391 U.S. 510, 88 S.Ct. 1770, 20 L.Ed.2d 776 (1968);
(2) that the Texas death penalty procedure is unconstitutional because it does not provide for jury instructions concerning mitigating circumstances;
(3) that the defendant’s constitutional rights were violated when the trial court permitted the prosecutor to comment on defense counsel’s failure to ask defense witnesses certain questions about the defendant’s reputation; and
(4) that the trial court’s refusal to instruct the jury on the law governing parole as it relates to persons sentenced to life imprisonment violated the defendant’s due process rights.
While we are compelled to recognize that O'Bryan has raised a serious challenge to the exclusion of two of the three jurors under Witherspoon, we conclude that the district court’s denial of habeas corpus relief should be affirmed.
I. FACTUAL AND PROCEDURAL BACKGROUND.
O’Bryan was convicted of murdering his eight-year-old son, Timothy, for remuneration or the promise thereof, namely, the proceeds from a number of life insurance policies on Timothy’s life. See Tex.Penal Code Ann. § 19.03(a)(3) (Vernon 1974).1 The facts of this case as adduced at trial are set forth in detail in the Texas Court of Criminal Appeals’ disposition of O’Bryan’s direct appeal. O’Bryan v. State, 591 S.W.2d 464 (Tex.Cr.App.1979) (en banc), cert. denied, 446 U.S. 988, 100 S.Ct. 2975, 64 L.Ed.2d 846 (1980). We have summarized them briefly here.
The record reflects that O’Bryan, who worked as an optician at Texas State Optical Company, had serious financial problems. The family was delinquent on a number of loans and had been forced to sell their home to meet their most pressing obligations. O’Bryan discussed his financial burdens with friends and acquaintances, informing some of them that he expected to receive some money by the end of the year. Despite his financial difficulties, O’Bryan substantially increased the life insurance coverage on his two children, Timothy and Elizabeth Lane, during 1974. By mid-October there was $30,000 worth of coverage on each child, while the coverage on O’Bryan and his wife was minimal.
In August, 1974, O’Bryan tried unsuccessfully to obtain cyanide where he worked. In September, he called a friend who worked at Arco Chemical Company, and the two discussed the varieties and availability of cyanide. O’Bryan continued to discuss cyanide among his fellow employees at Texas State Optical. Shortly before Halloween, O’Bryan appeared at Curtin Matheson Scientific Company, a chemical outlet in Houston. When he discovered that the company had cyanide available only in large quantities, O’Bryan asked the salesperson where he could obtain a smaller amount.
On Halloween, Thursday, October 31, 1974, the O’Bryan family dined at the home of the Bates family. The children of both families had planned to go “trick or treating” together in the Bates’ neighborhood. The defendant and Mr. Bates accompanied O’Bryan’s children and Bates’ son on the Halloween outing. When the party arrived at the Melvins’ home, the lights were out, but O’Bryan and the children went up to the home anyway. When no one answered the door, the children went on to the next house; O’Bryan remained behind for about thirty seconds. He then ran up to the children, “switching” at least two “giant pixy styx” in the air and exclaiming that “rich neighbors” were handing out expensive *370treats. O’Bryan offered to carry the pixy styx for the children. Back at the Bates’ home, O’Bryan distributed the pixy styx to his and Bates’ two children, and gave a fifth stick to a boy who came to “trick or treat” at the door.
After the Halloween festivities had been completed, O’Bryan took his children home, while his wife went to visit a friend. O’Bryan informed the children that they could each have one piece of candy before going to bed; Timothy chose the pixy stick. The boy had trouble getting the candy out of the tube, so O’Bryan rolled the stick in his hand to loosen the candy for his son. When Timothy complained that the candy had a bitter taste, O’Bryan gave him some Kool-Aid to wash it down.
Timothy immediately became ill and ran to the bathroom, where he started vomiting. When Timothy became sicker and went into convulsions, O’Bryan summoned an ambulance. Timothy died within an hour after he arrived at the hospital. Cyanide was found in fluids aspirated from his stomach and in his blood. The quantity of cyanide in the blood was well above the fatal human dose.
There was conflicting testimony at trial concerning the extent to which the defendant showed remorse at the hospital and at his son’s funeral. During the days following Halloween, O’Bryan gave conflicting stories as to the origin of the pixy styx, but he eventually claimed that the pixy styx came from the Melvin home. Mr. Melvin was at work, however, until late in the evening on Halloween.
O’Bryan was charged with and convicted of capital murder. At the sentencing proceeding, the State reintroduced the evidence that it had presented at trial and the defendant presented nine lay witnesses who stated that they did not believe that O’Bryan was likely to be a danger to society in the future. The jury answered the two special issues affirmatively2 and O’Bryan was sentenced to die.
O’Bryan’s conviction and sentence were affirmed by the Texas Court of Criminal Appeals on September 26,1979. O’Bryan v. State, supra. His application for a writ of certiorari to the United States Supreme Court was denied in 1980, O’Bryan v. Texas, 446 U.S. 988, 100 S.Ct. 2975, 64 L.Ed.2d 846 (1980), as was his first application for state habeas corpus relief.
In July, 1980, he filed a petition for federal habeas corpus relief, which was dismissed without prejudice so that he could return to state court to present additional unexhausted claims. His second application for state habeas corpus relief was denied on September 1, 1982, and his execution date set for October 31,1982. On September 29, 1982, O’Bryan filed his second application for federal habeas relief. The district court denied his application for the writ and stay of execution on October 20, 1982. Wé granted his application for a stay and request for a certificate of probable cause on October 27, 1982. O’Bryan v. Estelle, 691 F.2d 706 (5th Cir.1982).
II. THE WITHERSPOON ISSUE.
At least seventeen persons were excused for cause from serving on the jury on the basis of their opposition to the death penalty. O’Bryan challenges the exclusion of three of them: Jurors Wells, Pfeffer, and Bowman.
In Witherspoon v. Illinois, 391 U.S. 510, 88 S.Ct. 1770, 20 L.Ed.2d 776 (1968), the Supreme Court set aside a defendant’s death sentence where members of the venire had been excluded solely because they had conscientious scruples against capital punishment. The Court held that a potential juror could not be excused for cause on the basis of his opposition to the death penalty unless he was “irrevocably committed, before the trial has begun, to vote against the penalty of death regardless of the facts and circumstances that might emerge in the course of the proceedings.” *371Id. at 522 n. 21, 88 S.Ct. at 1777 n. 21. Such persons may be excluded only if they make it
unmistakably clear (1) that they would automatically vote against the imposition of capital punishment without regard to any evidence that might be developed at the trial of the case before them, or (2) that their attitude toward the death penalty would prevent them from making an impartial decision as to the defendant’s guilt.
Id. (emphasis in original). The Supreme Court reasoned that a jury from which all persons who had reservations against imposing the death penalty had been excluded was a jury “uncommonly willing to condemn a man to die.” Id. at 521, 88 S.Ct. at 1776.
Both the Supreme Court and this circuit have insisted upon strict adherence to the mandate of Witherspoon. The courts have required a death sentence to be set aside even if only one potential juror has been excluded for opposing the death penalty on grounds broader than those set forth in Witherspoon, see Davis v. Georgia, 429 U.S. 122, 97 S.Ct. 399, 50 L.Ed.2d 339 (1976); Marion v. Beto, 434 F.2d 29, 32 (5th Cir. 1970), regardless of whether the state has any peremptory challenges remaining at the close of voir dire. Alderman v. Austin, 663 F.2d 558, 564 n. 7 (5th Cir.1982), aff’d in relevant part, 695 F.2d 124 (5th Cir.1983) (en banc); Granviel v. Estelle, 655 F.2d 673, 678 (5th Cir.1981), cert. denied, 455 U.S. 1003, 102 S.Ct. 1636, 71 L.Ed.2d 870 (1982); Burns v. Estelle, 592 F.2d 1297, 1299 (5th Cir.1979), aff’d, 626 F.2d 396 (5th Cir.1980) (en banc); contra, Davis, supra, 429 U.S. at 124, 97 S.Ct. at 400 (Rehnquist, J., dissenting).
A. The Standard of Appellate Review.
As a threshold matter, we address the question of the appropriate standard of appellate review in federal habeas proceedings in assessing challenges to the exclusion of jurors in state trials under Witherspoon. The Supreme Court has never expressly stated what the standard of review of a Witherspoon challenge should be. Our review of the Supreme Court’s principal Witherspoon cases, Adams v. Texas, 448 U.S. 38, 49-51, 100 S.Ct. 2521, 2528-29, 65 L.Ed.2d 581 (1980); Lockett v. Ohio, 438 U.S. 586, 595-97, 98 S.Ct. 2954, 2959-61, 57 L.Ed.2d 973 (1978); Maxwell v. Bishop, 398 U.S. 262, 264-65, 90 S.Ct. 1578, 1580, 26 L.Ed.2d 221 (1970); Boulden v. Holman, 394 U.S. 478, 482-84, 89 S.Ct. 1138, 1140-42, 22 L.Ed.2d 433 (1969); Witherspoon, supra, suggests to us that in those cases, the Court was engaging in an independent or de novo review. By de novo review, we mean that the Court appears to decide for itself, based upon a reading of the transcript, whether a juror who was allegedly improperly excluded under Witherspoon has made it unmistakably clear that he or she would automatically vote against the imposition of the death penalty, without regard to any evidence that might be developed at trial, or that his or her attitude toward the death penalty would prevent him or her from making an impartial decision as to the defendant’s guilt. No deference appears to be given to the trial court’s ability to observe the demeanor of the juror, perhaps because Witherspoon’s requirement that a juror must make his or her views “unambiguously” or “unmistakably clear” suggests that there is no need for such deference. Significantly, however, the high Court’s decisions have generally been made in the context of a direct criminal appeal.3
Witherspoon challenges in the lower federal courts are raised in the context of federal habeas proceedings. In the traditional juror bias case, federal habeas review of a state trial court’s findings is more narrowly circumscribed than is appellate review in a direct criminal appeal. See Smith *372v. Phillips, 455 U.S. 209, 102 S.Ct. 940, 71 L.Ed.2d 78 (1982). In Smith, the petitioner maintained that a juror who had applied for a law enforcement position during the trial was presumptively biased against him. The state trial court held a post-trial hearing and determined that the juror had not been biased. The Supreme Court held that in a federal habeas action like the one before it, the state court’s findings with respect to actual bias were “presumptively correct under 28 U.S.C. § 2254(d),” and that “federal courts in such proceedings must not disturb the findings of state courts unless the federal habeas court articulate[d] some basis for disarming such findings of the statutory presumption that they are correct .... ” 102 S.Ct. at 946 (citing Sumner v. Mata, 449 U.S. 539, 101 S.Ct. 764, 66 L.Ed.2d 722 (1981)); see also Rogers v. McMullen, 673 F.2d 1185, 1190 n.10 (11th Cir.1982), cert. denied, - U.S. -, 103 S.Ct. 740, 74 L.Ed.2d 961 (1983); but see Irvin v. Dowd, 366 U.S. 717, 723, 81 S.Ct. 1639, 1642, 6 L.Ed.2d 751 (1961) (habeas case in which Supreme Court held that juror bias is “mixed [question of] law and fact” and therefore, it was duty of court of appeals to “independently evaluate the voir dire testimony of the impaneled jurors”) (quoting Reynolds v. United States, 98 U.S. 145, 156, 25 L.Ed. 244 (1878)). Since a Witherspoon challenge is a form of a challenge for juror bias, Smith would seem to indicate that a state court’s factual findings with respect to a juror’s willingness to impose the death penalty should be entitled to a presumption of correctness under section 2254(d). The Court’s requirement of strict adherence to Witherspoon, however, see, e.g., Davis v. Georgia, 429 U.S. 122, 97 S.Ct. 399, 50 L.Ed.2d 339 (1976) (death sentence must be set aside even if only one prospective juror is excluded in violation of Witherspoon), leaves us with some doubts about whether the Court would apply the traditional juror bias standard of review to a Witherspoon challenge. Further, the Supreme Court has not been entirely consistent in its treatment of the juror bias cases. Compare Smith, supra (presumption of correctness accorded state court’s findings with respect to actual bias), with Irvin, supra (juror bias is mixed question of law and fact to be independently reviewed by appellate court).
The State maintains that a state court’s factual findings are entitled to a presumption of correctness under section 2254(d) in Witherspoon challenges as well. See Alderman v. Austin, 695 F.2d 124, 130 (5th Cir. 1983)-(en banc) (Fay, J., dissenting); Darden v. Wainwright, 699 F.2d 1031, 1037-38 (11th Cir.), rehearing en banc granted, 699 F.2d 1043 (11th Cir.1983) (Fay, J., suggesting that Sumner presumption applies, but apparently engaging in independent review of the propriety of the state trial court’s exclusion of prospective jurors). Like the Supreme Court, however, the lower federal courts, without expressly establishing a standard of review, appear to engage in a de novo review of Witherspoon challenges in federal habeas proceedings. McCorquodale v. Balkcom, 705 F.2d 1553, 1556-57 n. 9 (11th Cir.1983); Bell v. Watkins, 692 F.2d 999, 1006-08 (5th Cir.1982); Williams v. Maggio, 679 F.2d 381, 384-86 (5th Cir.1982) (en banc), cert. denied,- U.S. -, 103 S.Ct. 3553, 77 L.Ed.2d 1399 (1983); Alderman v. Austin, 663 F.2d 558, 562-64 (5th Cir.1982), aff'd in relevant part, 695 F.2d 124 (5th Cir.1983) (en banc); Granviel v. Estelle, 655 F.2d 673, 677-78 (5th Cir.1981); Burns v. Estelle, 592 F.2d 1297, 1300-01 (5th Cir.1979), aff'd, 626 F.2d 396, 397-98 (5th Cir.1980) (en banc); Marion v. Beto, 434 F.2d 29, 31 (5th Cir.1970).
Some judges have suggested a third possibility: according some deference to the trial court’s decision in light of its opportunity to observe the juror’s demeanor while he or she is answering the questions on voir dire. Judge Kravitch recently suggested that where the questions asked of the prospective jurors are precise and closely track the language in Witherspoon, an appellate court’s deference to the trial court’s assessment of the clarity of the juror’s answers is appropriate. McCorquodale v. Balkcom, 705 F.2d 1553, 1561 (11th Cir.1983) (Kravitch, J., dissenting); see also Mason v. Balkcom, 487 F.Supp. 554, 560 (M.D.Ga.1980) (noting trial judge’s opportunity to observe *373and listen to juror, but engaging in independent analysis of Witherspoon challenge), rev’d on other grounds, 669 F.2d 222 (5th Cir.1982), cert. denied,- U.S. -, 103 S.Ct. 1260, 75 L.Ed.2d 487 (1983). The McCorquodale majority, however, carefully “scrutinized the record in [its own] effort to ascertain the correctness of the trial court’s finding with regard to a venireman’s convictions about capital punishment,” 705 F.2d at 1556-57, n. 9, and noted that in Aiken v. Washington, 403 U.S. 946, 91 S.Ct. 2283, 29 L.Ed.2d 856 (1971), the Supreme Court summarily reversed a death sentence where the state court had found no Wither-spoon violation and had accorded some deference to the trial court.
As discussed above, however, our review of the case law reveals that the courts have not specifically established a standard for appellate or collateral review of Wither-spoon challenges. While a state trial court’s factual findings with respect to jur- or bias may normally be entitled to a presumption of correctness in a federal habeas proceeding, Smith, supra, or at least to some deference in light of the trial court’s opportunity to observe the prospective juror during voir dire, the federal courts appear to engage in a de novo review of the trial court’s conclusions in cases where the defendant complains of a Witherspoon violation. Fortunately, we do not have to resolve the question whether and to what extent we should defer to the state court’s findings because we have concluded that even if we proceed under the more exacting standard resulting from de novo review, the trial judge’s exclusion of the three jurors in this case was proper under Witherspoon.
B. Juror Wells.
The first prospective juror excused for cause who has merited the defendant’s attention in these habeas proceedings was the Reverend Charles D. Wells. While Wells was able to imagine a case where a juror would vote to impose the death penalty, he was unable to see himself doing it, and on further questioning stated that he would automatically vote against the death penalty:
Q. Mr. Wells, I’m Mike Hinton, as the Court told you awhile ago for the State, and this is my co-counsel, Mr. Vic Driscoll. We come here representing the State of Texas in this case in which we are seeking as the punishment for this defendant the penalty of death.
Let me begin then by asking you whether or not you have any conscientious, moral or religious scruples against the imposition of the penalty of death in the electric chair?
A. Let me say that morally, I do, and I don’t think that I am capable of issuing a penalty of death to any man.
Q. All right. Again, as Judge Price told you a moment ago, no one is here to quarrel with your feelings and you certainly are entitled to your opinions as all of us are in our good country, and that includes your feelings about the death penalty. But under the law I must ask you this further additional question, Reverend, which is, I take it from your answer that you cannot imagine a case of murder where you could, as one of twelve jurors, vote to send someone to the electric chair as a punishment for their offense even though it was authorized by statute?
A. Would you repeat yourself now, please?
Q. Yes, sir. My question that I must ask you then, based upon your former answer is, I take it that because of the feelings that you do have that you are - entitled to have, moral feelings, religious feelings, that you cannot imagine a case where you, sitting on a jury, could vote to send someone to death in the electric chair as a punishment for their crime even though the law authorizes such penalty?
A. I can imagine it, but I can’t see myself doing it.
Q. All right. Then, I believe we must [be] somewhere between our hypothetical case where you can imagine a jury doing it?
*374A. Yes.
Q. But you can’t imagine yourself doing it as one of those jurors, is that correct, sir?
A. I can hardly see myself doing it, yes.
Q. All right. Now, I don’t want you to get angry with me and I’m not trying to argue with you, but I have to ask you for your answer, because this lady is taking down your testimony at this time for the record.
I take it then from your answer that because of your religious and moral principles and feelings that you are certainly entitled to have, you cannot imagine a case where you would vote for the imposition of death in the electric chair. Is that correct, sir?
A. No, I can’t.
MR. HINTON: I thank you, sir. We submit that the juror is not qualified, Your Honor.
EXAMINATION BY THE COURT
Q. Mr. Wells, let me ask you a question before they have the right to ask you questions.
Because of your moral or religious scruples, would you, if you were a member of the jury, would you automatically vote against the imposition of capital punishment no matter what the trial revealed?
A. As far as the electric chair is concerned?
Q. Would you personally, if you were a member of a jury, would you automatically vote against the imposition of the death penalty no matter what the trial revealed?
A. Yes, I would.
Q. All right.
> A. I would vote against it. dal Transcript at 763-66.
Texas, however, a juror does not tech-vote to impose the death penalty, ad, the trial judge sentences the deto die if, and only if, the jury two, sometimes three, statutory Sons in the affirmative. Following the examination by counsel for the State and by the court set forth above, counsel for the defendant directed Wells’ attention to those two questions:
Q. All right. You understand of course, nobody would ask you personally to put somebody to death. You understand that. You personally do not have to pull the switch or something?
A. I understand that.
Q. Surely. And of course there’s a lot of steps to go to between the time you start trial and the time you end the testimony and the defense puts on their testimony and of course, there’s a finding of guilt. You understand that. You do now if you haven’t before. Is that correct?
A. Yes.
Q. All right. And then, after a finding of guilt, if there is one, certain questions will be submitted to you as a juror. Now, are you saying at this time that under no circumstances, regardless of what the testimony would be, under no circumstances could you vote for the death penalty?
A. I don’t think there are any that I possibly could vote for the death penalty-
Q. All right. Let me ask you this, sir, if you were selected as a juror, even though the State has asked for the death penalty, could you consider these two issues — and I’ll ask you the issues that you would perhaps be asked to consider. All right?
A. All right.
Q. All right. The first issue would be whether the conduct of the defendant that caused the death of the deceased was committed deliberately and with the reasonable expectation that the death of the deceased or another would result. Could you answer that question, sir, after you had gotten all the facts?
A. Yes, Yes.
Q. You could answer that all right?
A. Yes.
*375Q. And that wouldn’t have any trouble with your conscience, would it?
A. No.
Q. Then of course there would be another question, and that would be whether there is [a] probability that the defendant would commit criminal acts of violence that would constitute a continuing threat to society. Now, could you possibly answer that question?
A. Yes, I possibly could answer that question.
Q. And would you have any quarrel or any problem with those questions?
A. I don’t think so.
Q. All right. And if you answered those questions, of course, it wouldn’t be up to you to do anything to this defendant. Those are merely questions that you answer to the Court. Isn’t that correct?
A. I would say yes.
Q. Could you do that, sir?
A. I could be as liberal in answering the questions as I could.
Q. And you would answer those questions truthfully, would you not?
A. Yes, as far as my opinions are concerned.
Q. I know you’re a minister, are you not?
A. Yes, sir. That’s correct.
Q. And you could answer those questions to the best of your ability and truthfully, could you not?
A. Yes.
2 Trial Transcript at 768-70. In spite of Wells’ assurance that he could and would answer the statutory questions, the trial court granted the State’s request that Wells be excused for cause. Significantly, at no time did defense counsel explain to Wells that if he and the other jurors answered the statutory questions in the affirmative, the trial judge would be required to sentence the defendant to death, and our review of the record indicates that at no point in the proceedings before the voir dire of Wells did the court or counsel render any such explanation. We thus do not know whether, in saying that he could and would answer the two statutory questions truthfully, Wells understood what the effect of those answers could be.
The Texas Court of Criminal Appeals was recently presented with a Witherspoon challenge involving a prospective juror whose views were in some respects strikingly similar to those of Wells. In Cuevas v. State, 641 S.W.2d 558 (Tex.Crim.App.1982) (en banc), venireman Ward initially stated, in the words of the court of criminal appeals, “that under no circumstances could he participate as a juror in returning a verdict that would require the court to assess the death penalty.” Id. at 560. After the “bifurcated system in Texas for assessing guilt and punishment in capital murder cases” had been “carefully” explained to him, however, and after he had been informed that the court, not the jury, would impose the penalty, Ward told the trial court that he could set aside his objections to capital punishment and answer the statutory questions on the basis of the evidence presented. Id4 *376While the court of criminal appeals relied on Adams, rather than Witherspoon, in setting aside Cuevas’ death sentence,5 the court was convinced that Ward could not have been excluded consistently with Witherspoon either, because “[h]e repeatedly stated that he could follow the law and convict upon proper evidence of guilt beyond a reasonable doubt, despite his opposition to the death penalty.” 641 S.W.2d at 563.
Cuevas sharpens the ultimate question presented by Wells’ exclusion. Just as a juror may be able to put aside his or her opposition to the death penalty and obey the law, so may he or she decide that he or she can determine the facts, i.e., answer the questions, as long as he or she is not the one who must actually pronounce the fatal words.6 If this is the juror’s conclusion, then he or she cannot be excluded under Witherspoon. Ward in Cuevas was just such a juror, and the Texas Court of Criminal Appeals held that his exclusion was error.
The threshold question presented by Wells’ voir dire is whether Wells had the same views as had Ward. The record indicates that he may have held those views. He stated that he could and would answer the statutory questions truthfully. But in view of the fact that the record does not contain an explanation to Wells of the effect of “yes” answers to those questions by the jury, we do not know from the record whether Wells, like Ward, could put aside his opposition to the death penalty and obey the law, i.e., answer the statutory questions truthfully, knowing the possible effect of his answers to those questions. We can only speculate. If the requirement of Witherspoon and its progeny — that a venireman must make “unmistakably clear” his or her inability to follow the law and abide by his or her oath, Adams, supra, 448 U.S. at 48, 100 S.Ct. at 2528; accord Boulden, supra, 394 U.S. at 483-84, 89 S.Ct. at 1141-42 — means that an appellate or federal habeas court that cannot be certain from the face of the record about a venireman’s inability to follow the law must, without any further consideration, grant the writ, then we would be compelled to do so here.
The State argues that we should not apply such a rule in the circumstances of this case. It maintains that it clearly established Wells’ automatic opposition to the death penalty during its initial examination of him. Having done so, the State argues that if the petitioner wished to rehabilitate Wells as a juror successfully, it was incumbent upon defense counsel to take his inquiry into Wells’ ability to answer the statutory questions one step further by clarifying, on the record, whether Wells understood the possible effect of his answers to those questions. The State argues that, since the defense failed to take that step, the exclusion of Wells on the basis of his initial unequivocal statements of automatic opposition to the death penalty was proper. We agree with the State.
A fair reading of Wells’ testimony in response to the initial questioning by the State and by the trial court indicates that Wells stated clearly, forcefully and without any equivocation that he would automatically vote against the imposition of the death penalty no matter what the trial revealed. Had the voir dire ended with the court’s questioning, the State would clearly have properly obtained the exclusion of Wells under Witherspoon. If the defense wished to rehabilitate Wells by demonstrating that he could obey the law regardless of his opposition to the death penalty, perhaps *377because of the distinction between the jury as the fact-finder and the judge as the sentencer that Ward found persuasive in Cuevas, then it was incumbent upon the defense to establish, on the record, Wells’ ability to engage in that fact-finding function with knowledge of the possible effect of those findings on the defendant’s fate. This the defense failed to do. Accordingly, we hold that the exclusion of Wells on the basis of his initial clear and unequivocal statements that he would automatically vote against the death penalty no matter what the trial revealed was proper under Witherspoon and its progeny.
This holding is not inconsistent with Burns, supra, in which we held that the exclusion of juror Doss was improper because we were forced to speculate about whether she could put aside her disbelief in the death penalty and follow the law. 592 F.2d at 1301. In Burns, Doss affirmed that she “did not believe in” the death penalty three times and stated “that the mandatory penalty of death or life imprisonment would ‘affect’ her ‘deliberations on any issue of fact in the case.’ ” Id. The trial court excluded Doss solely on the basis of those statements, and it rejected defense counsel’s suggestion that Doss be asked further questions because it could not imagine what else could have been asked. Unfortunately, we could:
She could have been asked whether, despite her expressed convictions, she could put her disbelief aside and do her duty as a citizen. Her answer might have been that she could. Or she could have been asked what effect the presence of a possible death sentence would have on her deliberations. Her answer might have been that she would wish to be very sure of guilt, to be thoroughly convinced, before she could find facts in such a way that the death penalty might result. Either answer would doubtless have rehabilitated her for jury service. An answer that she would not take or could not comply with the required oath not to be “affected” in her deliberations would doubtless, upon a proper definition of “affected” as meaning “disablingly” or “insurmountably” affected, have clearly disqualified her.
In contrast to the voir dire in Burns, neither the State nor the trial court has left us to speculate about the nature of Wells’ opposition to the death penalty. The prosecutor did not settle for Wells’ statement that he did not think that he was “capable of issuing the penalty of death to any man,” or that he could “imagine” but could not “see” himself voting to send someone to death. 2 Trial Transcript at 764-65. The prosecutor did not sit down until Wells had stated unequivocally that he could not imagine a case where he would “vote for the imposition of death.” Id. at 765. After the prosecutor had finished his questioning, the court took up the task and asked whether Wells would “automatically vote against the death penalty no- matter what the trial revealed,” to which Wells replied that he would. Id. at 766. If we are forced to speculate in this case, it is defense counsel, not the State or the trial judge, who failed to ask the necessary question.
Id. (emphasis in original). We went on to explain that the speculations caused by the inadequacy of Doss’ responses to the questions initially posed to her, in combination with the trial court’s failure to permit additional questioning by the defense, required us to hold that her exclusion was improper under Witherspoon:
To be sure, these are mere speculations about what her answers to such [additional] questions might have been. The point is that nothing in her actual answers forecloses them. Her mere acknowledgment that the penalty would “affect” her deliberations does not do so: what candid and responsible citizen would not admit as much, could truthfully swear the proposition to be one of no concern whatever?
Id.
We have here the converse of the situation in Burns. Nothing in Wells’ answers to defense counsel’s questions forecloses the possibility that he would not have answered the statutory questions on the basis of the evidence if he knew that an affirmative *378answer to both questions would mandate the defendant’s execution. The State established Wells’ unequivocal opposition to the death penalty beyond speculation; it was then incumbent upon the defendant, if he wished to rehabilitate the juror, to ask enough questions to demonstrate that Wells could perform his fact-finding function in spite of his opposition to the death penalty.7
We were recently confronted with a similar failure by defense counsel to rehabilitate a juror who had expressed her opposition to the death penalty in Porter v. Estelle, 709 F.2d 944 (5th Cir.1983). In Porter, in response to the State’s questions, prospective juror Herndon had repeatedly expressed “longstanding convictions against the death penalty that would [have] require^] her to vote against [it] no matter what the trial revealed.” 709 F.2d at 948. She maintained her opposition in response to two questions from defense counsel but when asked whether she could “put her convictions aside and do her duty ‘as a Juror in a Capital Murder case,’ ” she replied that she could. Id. (emphasis in original). When defense counsel objected to the State’s challenge for cause, the State pointed out that the general question asked about Herndon’s ability to do her “duty as a juror” had not included “the second predicate question in Burns .... [that] if it meant sentencing a man to death, could you follow that duty?’ ” Id. Defense counsel did not ask any more questions and the juror was excused for cause. We held in Porter that
[i]n view of Herndon’s repeated, firm, and unequivocal statements of irrevocable [opposition to the] imposition of the death penalty under any circumstances, we are unable to say her limited reply that “she could do her duty as a juror ” indicated any vacillation or equivocation in her previous statement of unalterable opposition to imposition of the death penalty.
709 F.2d at 948-49 (emphasis in original). Like the defense counsel in Porter, defense counsel here did not ask enough questions to demonstrate that Wells’ previously expressed unequivocal opposition to the death penalty would not prevent him from performing his function as a juror in a capital case.
C. Juror Pfeffer.
Juror Pfeffer presents the opposite problem from Wells. Indeed, the voir dire of Pfeffer may be the quintessential example of a situation in which it would be appropriate for an appellate court to give at least some deference to the trial judge, who has had the opportunity to observe the juror as he or she struggles to give an honest answer to difficult questions. Regardless of whether such deference is advisable, our own independent review of the record indicates that Pfeifer’s exclusion was not in violation of Witherspoon.
As we observed in our decision to grant O’Bryan a stay of execution, and as the court of criminal appeals recognized, during the initial two-thirds of Pfeifer’s lengthy voir dire examination (covering twenty-four pages in the transcript), he was
equivocal in stating his position on capital punishment. He described himself as a “borderline thinker” on the issue of capital punishment, and expressed doubt that he could make the proper judgment because of his “mixed feelings” concerning the infliction of the death penalty.
O’Bryan v. Estelle, 691 F.2d 706, 709 (5th Cir.1982). When informed by the trial court that he must give a definitive answer, Pfeffer stated that he “would have to say” that he could not vote to impose the death penalty, although he continued to add caveats from time to time, referring to the necessity for giving the judge a “yes or no *379answer,” “to give a correct answer,” or “for the good of everyone concerned:”
THE COURT: Well, the law requires that we have to have a definite answer.
JUROR PFEFFER: I understand, right.
THE COURT: Because the law does allow people to be excused because of certain beliefs that could be prejudicial or biased for one side or the other, and both sides just want to know if you can keep an open mind, consider the entire full range of punishment, whatever that may be, and under the proper set of circumstances, if they do exist and you feel they exist, that you could return that verdict. And that’s in essence what they’re asking.
JUROR PFEFFER: Indirectly, I guess I would have to say no.
THE COURT: You could not?
JUROR PFEFFER: I would have to say no then, to give you a yes or no answer.
THE COURT: Then, am I to believe by virtue of that answer that regardless of what the facts would reveal, regardless of how horrible the circumstances may be, that you would automatically vote against the imposition of the death penalty?
JUROR PFEFFER: As I say, I don’t know.
THE COURT: Well, that’s the question I have to have a yes or no to.
JUROR PFEFFER: Right.
THE COURT: And you’re the only human being alive who knows, Mr. Pfeffer.
JUROR PFEFFER: Right, I understand. If I have to make a choice between yes and no, I would say that I couldnt make the judgment.
3 Trial Transcript at 882-84. Although Pfeffer interspersed his answers from this point on in his voir dire with caveats or qualifications such as those referred to above, there are at least two instances in which, if we focus on a specific question and answer, he gave unqualified answers:
THE COURT: You yourself are in such a frame of mind that regardless of how horrible the facts and circumstances are, that you would automatically vote against the imposition of the death penalty? Is that correct?
JUROR PFEFFER: Well, if it says a yes or no, I would have to say yes, I would automatically vote against, to give a correct answer.
THE COURT: You would vote against?
JUROR PFEFFER: Yes.
3 Trial Transcript at 884-85 (emphasis added).
Q. (By Mr. Harrison) Then, under no circumstances, Mr. Pfeffer, could you even think of voting or answering those questions if the result of those questions were to be to, in effect, give somebody the death penalty. Is that correct?
A. I think at the present time that’s correct, yes.
Id. at 892.
In O’Bryan’s view, while Pfeffer had “reservations” or “mixed emotions” about the death penalty, and while he was seriously concerned about his own ability to assess the death penalty, he was willing to do so in a “very, very extreme set of circumstances.”8 If this were an accurate *380view, then Pfeffer’s exclusion would have been improper. In Witherspoon, one of the venirewomen excluded stated that “she would not ‘like to be responsible for ... deciding somebody should be put to death.’ ” 391 U.S. at 515, 88 S.Ct. at 1773. In the footnote accompanying this description of the juror’s feelings, the Supreme Court cited, apparently with approval, a Mississippi case that reversed a trial court’s exclusion of jurors who did not wish to decide whether a person should die:
The declaration of the rejected jurors, in this case, amounted only to a statement that they would not like ... a man to be hung. New men would. Every right-thinking man would regard it as a painful duty to pronounce a verdict of death upon his fellow-man.
Id. at 515 n. 8, 88 S.Ct. at 1773 n. 8 (quoting Smith v. State, 55 Miss. 410, 413-14 (1887)); accord Burns, supra, 592 F.2d at 1299 n. 2. Witherspoon makes it clear that neither a deep reluctance to pronounce the death penalty, short of absolute refusal to do so, nor the reservation of the death penalty for only an extreme set of circumstances, is a ground for exclusion.9 391 U.S. at 522 n. 21, 88 S.Ct. at 1777 n. 21.
A careful review of the transcript indicates that during the initial two-thirds of Pfeffer’s voir dire, he did indeed suggest that he would be able, in an extreme set of circumstances, to assess the death penalty. At that point, however, Pfeffer’s attitude, or at the very least, his answers, changed when he stated that “if [he had] to make a choice between yes and no,” 3 Trial Transcript at 884, he would have to say that he *381would automatically vote against imposition of the death penalty. We conclude that this case is controlled by our en banc decision in Williams v. Maggio, 679 F.2d 381 (5th Cir.1982) (en banc), cert. denied, - U.S.-, 103 S.Ct. 3553, 77 L.Ed.2d 1399 (1983). Juror Brou in Williams stated that there were “certain cases where you read about them and they are so hideous that you just think, oh, the death penalty would be the only good outcome,” 679 F.2d at 305, a statement similar to Pfeifer’s statement that he could assess the death penalty in a “very, very extreme set of circumstances.” The prosecutor continued his probing, however, and in response to a leading question about Williams’ particular case, Brou stated that she felt that she could not impose the death penalty:
Q. So you feel that you could not return the death penalty?
A. (Ms. Brou) No.
Id. (emphasis in majority opinion).10
Viewing Brou’s initial uncertainty in conjunction with her ultimate response to the prosecutor’s question about her ability to return the death penalty, the majority of this court concluded in Williams that “the record of [Brou’s] automatic opposition to the death penalty [was] established.” Id. The en banc majority specifically rejected the contention that under Witherspoon “exclusion of a venireman is impermissible unless he states in response to all questions that he absolutely refuses to consider the death penalty.” 679 F.2d at 386 (emphasis added). It would seem that under Williams, it is the juror’s ultimate conclusion about whether he or she is irrevocably opposed to the death penalty that is critical. Absent effective rehabilitation of the sort that we found lacking in defense counsel’s questioning of Wells and the Texas Court of Criminal Appeals found present in Cuevas, a juror’s ultimate statement of unequivocal opposition to the death penalty will justify his or her exclusion under the Williams court’s interpretation of Wither-spoon.
Pfeifer’s unequivocal statement that he would automatically vote against the death penalty, 3 Trial Transcript at 885, was sufficient to justify his exclusion under Williams; his earlier statement that he could assess the death penalty in an ex*382treme set of circumstances, his prolonged uncertainty and his caveats and qualifications preceding that unequivocal statement do not undercut the validity of that exclusion. The caveats and qualifications following that unequivocal statement do not amount to the kind of effective rehabilitation of Pfeffer that would be necessary for us to hold that his exclusion was error.
O’Bryan suggests that Pfeifer’s ultimate statements do not accurately reflect Pfeffer’s position. O’Bryan contends that the trial judge mistakenly viewed Witherspoon as an “exclusionary rule,”11 and that the judge was unwilling to accept Pfeifer’s deep, agonized reluctance to pronounce the death penalty. The defendant maintains that the trial court, in effect, coerced Pfeffer into taking a position that he would automatically vote against the imposition of the death penalty regardless of the facts established at trial. Our review of the entire voir dire, encompassing seven volumes of the trial record, indicates that the trial judge did not generally view Witherspoon as an exclusionary rule. Instead, he painstakingly questioned, and permitted counsel to question, each and every juror who expressed discomfort about imposing the death penalty, excluding some for cause but refusing to exclude others, thereby forcing the State to exercise its peremptory challenges.
We cannot say that the court’s probing of Pfeifer’s answers in an attempt to find some basis on which to evaluate his true feelings was improper. Throughout the voir dire, Pfeffer continued to express concern about his ability to pronounce the death penalty. The trial judge may have thought that Pfeifer’s professed willingness to assess the death penalty in a “very, very extreme set of circumstances” was a smoke screen for what was really an inability to assess the death penalty under any circumstance. Under this view, we would have to say that a trial judge, harboring those suspicions about the person in front of him or her, has the right, within certain limitations, to pursue a line of questioning designed to flush out the venireman’s true views. Indeed, an appellate court confronted with the question whether such an exclusion was proper, and with the apparent necessity of making an independent review based on the cold record, will expect no less. The trial court in this case succeeded in obtaining an answer from Pfeffer that he could not impose the death penalty. Under these circumstances, we cannot say that Pfeifer’s exclusion was improper. Williams, supra.
D. Juror Bowman.
O’Bryan’s final complaint about the voir dire involves the exclusion of juror Bowman. Like Pfeffer, Bowman was originally unsure of his feelings about the death penalty, but on further questioning he stated that he could not vote for it. When asked about a crime “closer to home,” however, he said that he could consider the death penalty if the victim “was one of [his] family.” 3 Trial Transcript at 918.
We agree with the Texas Court of Criminal Appeals that Bowman’s response that he could impose the death penalty if a member of his family had been killed does not invalidate the trial court’s excusal of him for cause. If the victim had been a member of Bowman’s family, he would have been “unable to serve as a juror because of his interest and prejudice in the case.” O’Bryan, supra, 591 S.W.2d at 473 (citing Tex.Code Crim.Pro.Ann. art. 35.16 (Vernon 1966 & Supp.1983)). The statement that a person could impose the death penalty only in a case in which he or she would not be permitted to serve is virtually the equivalent of a statement that the juror would never vote in favor of capital punishment.
III. THE CONSTITUTIONALITY OF THE CAPITAL SENTENCING PROCEDURE.
O’Bryan contends that the Texas capital sentencing procedure, Tex.Code Crim.Pro. *383Ann. art. 37.071 (Vernon 1981), is unconstitutional because it does not provide for instructions to the jury concerning mitigating circumstances.12 He argues that in the absence of such instructions, the determination of punishment is left to the unbridled discretion of the jury, resulting in the imposition of the death penalty in an arbitrary and capricious manner, in violation of the eighth and fourteenth amendments. See Furman v. Georgia, 408 U.S. 238, 92 S.Ct. 2726, 33 L.Ed.2d 346 (1972). Relying on the Supreme Court’s holdings in Eddings v. Oklahoma, 455 U.S. 104, 102 S.Ct. 869, 71 L.Ed.2d 1 (1982), that a sentencer must consider all of the mitigating evidence before sentencing someone to die, and in Lockett v. Ohio, 438 U.S. 586, 98 S.Ct. 2954, 57 L.Ed.2d 973 (1978), that the sentencer cannot be precluded from considering any mitigating factors, O’Bryan maintains that an instruction concerning mitigating evidence is constitutionally mandated.
The State claims that O’Bryan cannot be heard to complain about the trial court’s failure to give a jury instruction on mitigating circumstances because he did not make a contemporaneous objection to the court’s charge on this ground or request such an instruction at trial, as required by state law. Tex.Code Crim.Pro.Ann. arts. 36.-14, .15 (Vernon 1981, superseded). It is, of course, settled law that “when a procedural default bars state litigation of a constitutional claim, a state prisoner may not obtain federal habeas relief absent a showing of cause and actual prejudice.” Engle v. Isaac, 456 U.S. 107, 129, 102 S.Ct. 1558, 1572, 71 L.Ed.2d 783 (1982); accord, Wainwright v. Sykes, 433 U.S. 72, 97 S.Ct. 2497, 53 L.Ed.2d 594 (1977). On the other hand, we are not “barred from reviewing a claim by a state procedural rule when the state courts themselves have not followed the rule.” Bell v. Watkins, 692 F.2d 999, 1004 (5th Cir.1982); accord, Ulster County Court v. Allen, 442 U.S. 140, 154, 99 S.Ct. 2213, 2223, 60 L.Ed.2d 777 (1979); Henry v. Wainwright, 686 F.2d 311, 313 (5th Cir. 1982). The problem here is that the state court did not say whether it was denying the petitioner habeas corpus relief on the basis of his procedural default or on the merits of his claim; it simply denied his petition without comment.13
*384We were recently confronted with the problem of interpreting a state court’s silence with respect to the grounds for its denial of a state habeas petitioner’s claim in Preston v. Maggio, 705 F.2d 113 (5th Cir. 1983). We determined that the same considerations should be applied to cases in which the state court has denied relief without offering any reasons for its denial as are applied to cases where a state court has been “less than explicit.” Id. at 116. We included among those considerations:
Whether the court has used procedural default in similar cases to preclude review of the claim’s merits, whether the history of the case would suggest that the state court was aware of the procedural default, and whether the state court’s opinions suggest reliance upon procedural grounds or a determination of the merits.
Id. (citing Ulster County Court, supra, 442 U.S. at 147-54, 99 S.Ct. at 2219-23). Applying the Preston criteria to O’Bryan’s case, we conclude that the state court presumably denied his claim on the basis of his procedural default.
The Texas courts have held that in the absence of objections to the charge or a specially requested charge, no errors therein can be considered on appeal “unless it appears that the defendant has not had a fair and impartial trial.” Boles v. State, 598 S.W.2d 274, 278 (Tex.Cr.App. 1980). And, in determining whether fundamental error is present, it is proper to view the charge as a whole.
White v. State, 610 S.W.2d 504, 506 (Tex.Cr. App.1981) (en banc). In Williams v. State, 622 S.W.2d 116 (Tex.Cr.App.1981) (en banc), cert. denied, 455 U.S. 1008, 102 S.Ct. 1646, 71 L.Ed.2d 876 (1982), the Texas Court of Criminal Appeals refused to hear a capital murder defendant’s contention that he was entitled to a mitigating circumstances instruction during the sentencing phase of his trial where he had failed to object or request such an instruction at trial. The court held: “Absent such an objection or requested instruction, the trial court’s failure to charge the jury as to the consideration of mitigating circumstances was not reversible error.” Id. at 120. Williams’ position was the same as O’Bryan’s: Williams contended that his death sentence had been imposed unconstitutionally because the jury had not been given a mitigating circumstances instruction, but he had never requested such an instruction at trial. Under these circumstances, the Texas court concluded that Williams’ procedural default precluded review of his constitutional claim. O’Bryan has not offered us any indication that the court would not have made the same decision here.14 Further, we know that the Texas Court of Criminal Appeals had been made aware of O’Bryan’s procedural default, since the State raised the matter in its answer opposing the petitioner’s second application for habeas relief.
O’Bryan argues that his failure to object to the trial court’s charge should not bar his claim because the Texas court’s decisions in Williams, supra, and Quinones v. State, 592 S.W.2d 933 (Tex.Cr.App.) (en banc), cert. denied, 449 U.S. 893, 101 S.Ct. 256, 66 L.Ed.2d 121 (1980), placed him in a “Catch-22” situation. As discussed above, the court of criminal appeals held in Williams that it would not review a challenge *385to the sentencing instructions where the defendant had made no objection to those instructions at trial. In Quinones, the defendant had requested and been denied a charge on mitigating circumstances. The court of criminal appeals held that no such charge was necessary and overruled his exception:
Appellant was entitled to present evidence of any mitigating circumstances and did present such evidence, including a broad discussion of his personal and family background. The question then is whether the language of the special issue is so complex that an explanatory charge is necessary to keep the jury from disregarding the evidence properly before it. In King v. State, 553 S.W.2d 105 (Tex.Cr. App.1977), cert. denied, 434 U.S. 1088, 98 S.Ct. 1284, 55 L.Ed.2d 793 (1978), this Court held that the questions in Art. 37.-071 used terms of common understanding which required no special definition. The jury can readily grasp the logical relevance of mitigating evidence to the issue of whether there is a probability of future criminal acts of violence. No additional charge is required.
Id. at 947. Contrary to O’Bryan’s assertion, these two decisions do not present him with a Catch-22 situation, since they do not hold that a trial judge may not give a mitigating circumstances instruction if he or she is disposed to grant the defendant’s request. The purpose of a contemporaneous objection requirement is to give the trial judge the opportunity to rule on the defendant’s constitutional claim, see Engle v. Isaac, 456 U.S. 107, 128-29, 102 S.Ct. 1558, 1572, 71 L.Ed.2d 783 (1982); this is what O’Bryan failed to do.15
Accordingly, we hold that the defendant is barred from raising his claim about the absence of a mitigating circumstances instruction in these federal habeas proceedings. See also O’Bryan v. Estelle, 691 F.2d, 706, 710 (5th Cir.1982) (Gee, J., dissenting). We note further that the Supreme Court’s recent decision in Zant v. Stephens, - U.S. -, 103 S.Ct. 2733, 2744, 77 L.Ed.2d 235 (1983) (holding that death sentence need not be set aside where one of three statutory aggravating circumstances found by juror was subsequently held to be invalid by state supreme court but other two were specifically upheld, and stating that “the absence of legislature or court-imposed standards to govern the jury in weighing the significance of either or both of those aggravating circumstances does not render [capital sentencing statute] invalid” as applied) makes the defendant’s argument on the merits far more difficult.
*386O’Bryan also contends that his punishment of death, based solely upon the evidence introduced at the guilt stage of trial, the state having elected to present no evidence bearing upon the special issue required by article 37.071(b)(2), V.A.C.C.P., violated the plurality conclusion in Furman v. Georgia, 408 U.S. 238 [92 S.Ct. 2726, 33 L.Ed.2d 346] (1972); Woodson v. North Carolina, 428 U.S. 280 [96 S.Ct. 2978, 49 L.Ed.2d 944] (1976); Roberts v. Louisiana, 428 U.S. 325 [96 S.Ct. 3001, 49 L.Ed.2d 974] (1976).
The defendant never explains precisely what he means by this statement, but it seems to refer to the contention that he made in his direct criminal appeal that the evidence was insufficient to support the jury’s finding that there was a probability that he would commit criminal acts of violence that would constitute a continuing threat to society. O’Bryan v. State, supra, 591 S.W.2d at 480.16 We agree with the Texas Court of Criminal Appeals that the State’s reintroduction of the evidence presented during the guilt phase of the trial provided sufficient evidence of O’Bryan’s future dangerousness to support the jury’s findings.17 In particular, we note that O’Bryan carefully planned the poisoning of his own son so that he could collect life insurance proceeds, and that he gave the poisoned pixy styx to four other children, including his own daughter, in an attempt to cover up his crime. We cannot say that no rational trier of fact could have found beyond a reasonable doubt that such a man posed a continuing threat to society. See note 18.
IV. PROSECUTORIAL ARGUMENT.
O’Bryan complains that his constitutional rights were violated when the prosecutor was permitted to comment, during closing argument at the sentencing phase of the trial, on defense counsel’s failure to question defense witnesses concerning O’Bryan’s reputation for being a peaceful and law-abiding citizen, and to suggest that counsel had a “moral obligation” to ask this question of the witnesses. O’Bryan contends that these comments impermissibly shifted the burden of disproving future dangerousness onto the defendant, and that the prosecutor’s comments deprived him of a fundamentally fair trial.18
The trial court overruled O’Bryan’s objection to the prosecutor’s argument. The court stated that a party is permitted, in Texas, to comment on the failure to call certain witnesses. The Texas Court of Criminal Appeals agreed, noting that it “is well settled that the prosecutor, in argument, may comment upon the defendant’s failure to call certain witnesses.” O’Bryan v. State, 591 S.W.2d 464, 479 (Tex.Cr.App. 1979) (en banc), cert. denied, 446 U.S. 988, 100 S.Ct. 2975, 64 L.Ed.2d 846 (1980) (citing, e.g., Carrillo v. State, 566 S.W.2d 902, 912 (Tex.Cr.App.1978)). The court added that while the burden of proving the special issues is on the State, “the option of coming *387forward with mitigating circumstances is upon the capital defendant.” 591 S.W.2d at 479. Noting that counsel for both the defense and the prosecution had commented on the failure to call witnesses,19 and that the trial court had properly charged the jury with regard to the State’s burden of proof during the punishment phase of the trial, the Texas Court of Criminal Appeals held that the prosecutor’s remarks had not shifted the burden of proof to the defendant, and that the trial court’s ruling was not in error. Id.
Our review of the propriety of prosecutorial comments made during a state trial is “the narrow one of due process, and not the broad exercise of supervisory power that [we] would possess in regard to [our] own trial court.” Donnelly v. DeChristoforo, 416 U.S. 637, 642, 94 S.Ct. 1868, 1871, 40 L.Ed.2d 431 (1974). In the absence of a violation of a specific guarantee of the Bill of Rights,20 we may overturn a state court conviction only if the complained-of conduct has made the trial fundamentally unfair. Id. at 645, 94 S.Ct. at 1872; see also Passman v. Blackburn, 652 F.2d 559, 567 (5th Cir.1981), cert. denied, 455 U.S. 1022, 102 S.Ct. 1722, 72 L.Ed.2d 141 (1982); Cobb v. Wainwright, 609 F.2d 754, 756 (5th Cir.), cert. denied, 447 U.S. 907, 100 S.Ct. 2991, 64 L.Ed.2d 857 (1980). Such is not the case here.
The prosecutor’s remarks did not impermissibly shift the burden of proving the special issues under Tex.Code Crim.Pro. Ann. art. 37.071 (Vernon 1981). The prosecutor’s comments were at most tangentially related to the burden of proof. The cases cited by the defendant as examples of impermissible burden-shifting involved specific instructions by the trial court about who bore the burden of proving certain issues, see, eg., Sandstrom v. Montana, 442 U.S. 510, 99 S.Ct. 2450, 61 L.Ed.2d 39 (1979), or a state statute establishing the same. In re Winship, 397 U.S. 358, 90 S.Ct. 1068, 25 L.Ed.2d 368 (1970). Here the complaint is about a prosecutor’s off-the-cuff comments, not judicial instructions.
In Cupp v. Naughten, 414 U.S. 141, 94 S.Ct. 396, 38 L.Ed.2d 368 (1973), the habeas petitioner claimed that a state trial judge’s instruction that “[e]very witness is presumed to speak the truth,” id. at 142, 94 S.Ct. at 398, impermissibly shifted the burden of proof. The Supreme Court held that “[w]hatever tangential undercutting of [the presumption of innocence and the state’s duty to prove guilt beyond a reasonable doubt] may, as a theoretical matter, have resulted from the giving of the instruction on the presumption of truthfulness is not of constitutional dimension.” Id. at 149, 94 S.Ct. at 401. The connection between the prosecutor’s comments about the failure to question defense witnesses in this case and the burden of proof is even more attenuated than was the connection in Naughten, supra.
Further, we have held that the requirements of the federal Constitution are satisfied as long as the State bears the burden of proving the aggravating circumstances. Gray v. Lucas, 677 F.2d 1086, 1107 (5th Cir.1982), cert. denied,-U.S.-, 103 S.Ct. 1886, 76 L.Ed.2d 815 (1983). The trial court instructed the jury that the prosecution bore the burden of proving the defendant’s future dangerousness beyond a reasonable doubt. The Constitution requires no more. The question of who should produce evidence of mitigating circumstances was a matter of state law; the state court’s decision that the defendant bore that burden entailed no constitutional violation. See Gray, supra.
We find no error of constitutional magnitude, if there be any error at all, in the trial court’s permitting the prosecution to comment on the defendant’s failure to ask his witnesses certain questions. As the Texas Court of Criminal Appeals noted, the prosecutor may comment, as a matter of *388state law, on the defendant’s failure to call a material witness, and he may draw an inference from that failure that the testimony would have been unfavorable. See, e.g., Carrillo, supra. Similarly, we have held that in federal court, “the failure of a party to produce as a witness one peculiarly within the power of such party creates an inference that such testimony would be unfavorable, and may be the subject of comment to the jury by the other party.” United States v. Lehmann, 613 F.2d 130, 136 (5th Cir.1980) (quoting McClanahan v. United States, 230 F.2d 919 (5th Cir.), cert. denied, 352 U.S. 824, 77 S.Ct. 33, 1 L.Ed.2d 47 (1956)). Comment is not permissible, however, if the “person in question is equally available to both parties; particularly where he is actually in court.” Id.
O’Bryan did call these witnesses, and he points out that the prosecutor could have asked them about the defendant’s reputation for peacefulness as easily as the defendant could have. The prosecutor’s statement that defense counsel had a “moral obligation” to ask certain questions of the witnesses probably bordered on the improper. Viewing these two comments in the context of the trial as a whole, however, see Houston v. Estelle, 569 F.2d 372, 377 (5th Cir.1978), we cannot say that they deprived the defendant of a fundamentally fair trial.
In Houston, supra, where we set aside a state court conviction on the basis of improper prosecutorial comments, the prosecutor had repeatedly made the remarks even after he was reprimanded by the trial judge. Further, the comments themselves were far more egregious than those made during O’Bryan’s trial. The prosecutor began his argument with a personal attack on the integrity of defense counsel, continued with a personal opinion about the defendant’s credibility on the witness stand, and suggested that the jury give the defendant a long sentence so that the defendant would have an opportunity to rehabilitate himself, a suggestion that was improper under state law. 569 F.2d at 378, 380, 381 n. 12. In contrast, the Supreme Court refused to set aside a defendant’s conviction where the prosecutor had expressed his personal opinion about the defendant’s guilt and had made an improper suggestion about the defendant’s motives for standing trial. Donnelly v. DeChristoforo, 416 U.S. 637, 642, 94 S.Ct. 1868, 1871, 40 L.Ed.2d 431 (1974). In O’Bryan’s case, the State’s evidence, adduced at the guilt phase of trial, of the probability of the defendant’s future dangerousness was substantial, and the comments’ potential for prejudice was at best minimal. Accordingly, we hold that the prosecutor’s comments do not entitle O’Bryan to federal habeas relief.
V. PAROLE INSTRUCTIONS.
Under Texas law, a jury may not consider the possibility of parole in its deliberation on punishment, see, e.g, Moore v. State, 535 S.W.2d 357 (Tex.Cr.App.1976), and the jury in 0*Bryan’s case was so instructed.21 The defendant maintains that the trial court’s refusal to instruct the jury about the law governing the Board of Pardons and Paroles in relation to inmates sentenced to life imprisonment deprived him of a fundamentally fair trial in violation of the due process clause of the fourteenth amendment. Relying on People v. Morse, 60 Cal.2d 631, 388 P.2d 33, 36 Cal. Rptr. 201 (1964), O’Bryan argues that an instruction about the law of parole is necessary in a capital case to dispel the widely held misconception that a life sentence will result in a defendant’s only serving nine or ten years in prison. The Texas Court of Criminal Appeals declined to adopt the view of the California courts that a jury should be charged on the law of parole and then instructed not to consider it. O’Bryan, supra, 591 S.W.2d at 478.
As in our review of alleged prosecutorial misconduct, our review of a *389challenge to instructions given in a state criminal trial is narrowly limited to whether the alleged impropriety “so infected the entire trial that the resulting conviction violates due process.” Cupp v. Naughten, 414 U.S. 141, 147, 94 S.Ct. 396, 400, 38 L.Ed.2d 368 (1973); accord, Easter v. Estelle, 609 F.2d 756, 758 (5th Cir.1980); Higgins v. Wainwright, 424 F.2d 177 (5th Cir. 1970). Morse, supra, was a response to California’s earlier minority position permitting the jury to consider parole in determining punishment. Concluding that the evidence concerning parole introduced at trials was confusing to the jurors, the California Supreme Court decided that a jury should be informed about the parole law and then told not to consider parole in making its determination on punishment. The California court’s decision was based on its supervisory powers over the state trial courts, not on the United States Constitution. Whatever the reasons for a state court’s decision to require such an instruction in its own trial courts, we cannot say that an instruction on parole is constitutionally mandated in a capital case. See California v. Ramos,- U.S. -, -, 103 S.Ct. 3446, 3448, 77 L.Ed.2d 1171 (1983) (instruction informing jurors in capital case that governor has power to commute “life sentence without possibility of parole” but not informing them of equivalent power to commute death sentence not unconstitutional).
Since the failure to give such an instruction did not deprive O’Bryan of a fundamentally fair trial, his complaint about the court’s instruction is not cognizable in federal habeas proceedings. See Easter, supra.
VI. CONCLUSION.
We hold:
1. that jurors Wells, Pfeffer and Bowman were not excluded in violation of Witherspoon v. Illinois, 391 U.S. 510, 88 S.Ct. 1770, 20 L.Ed.2d 776 (1968), because at some point during the voir dire, each made it unmistakably clear that he could not vote for the death penalty no matter what the law required;
2. that O’Bryan’s failure to request an instruction concerning mitigating circumstances at trial precludes him from challenging the court’s failure to give such an instruction in these proceedings;
3. that the prosecutor’s comments about the defendant’s failure to ask certain questions of defense witnesses did not deprive the defendant of a fundamentally fair trial; and
4. that O’Bryan’s complaint about the trial judge’s refusal to give an instruction concerning Texas parole law is not cognizable in federal habeas proceedings.
Accordingly, the federal district court’s denial of habeas relief to O’Bryan is AFFIRMED.
. The Texas Penal Code provides in relevant part:
(a) A person commits an offense if he commits murder as defined under Section 19.-02(a)(1) of this code and:
(3) the person commits the murder for remuneration or the promise of remuneration or employs another to commit the murder for remuneration or the promise of remuneration;
(b) An offense under this section is a capital felony. Tex.Penal Code Ann. § 19.03(a)(3)(b) (Vernon 1974).
. A Texas trial judge must sentence a defendant to die if the jury returns affirmative answers to two, sometimes three, special interrogatories. See Tex.Code Crim.Pro.Ann. art. 37.071 (Vernon 1981) (set forth in relevant part at note 12).
. While Maxwell, supra, and Boulden, supra, were federal habeas cases, the Supreme Court did not ultimately decide whether a Wither-spoon violation had occurred in either case because it was not satisfied that the Wither-spoon issue had been raised in the federal or state courts below. Accordingly, the Court remanded both cases to the lower federal courts for further consideration, and if necessary, exhaustion of state remedies.
. The relevant portion of the voir dire is set forth in the Court of Criminal Appeals’ opinion:
Q.....
Now, you have expressed an objection to the death penalty. Would you feel that your conscientious objection to the death penalty as such, that it would affect your deliberation upon his guilt in the first instance or on either of the questions of fact, on those questions that I asked?
A. No.
Q. Well, now you have answered me two different ways.
A. Maybe I misunderstood you.
Q. I asked you at the outset whether you could participate as a juror in returning a verdict that would require the infliction of death as a punishment for crime.
A. Oh, I see.
Q. And you expressed an opinion that you could not.
A. May I ask a question? You say it’s the Court and not the jury that imposes the penalty, is that right?
Q. That’s right, but the Court is obligated to assess punishment based on the answers to those special issues____ Would your attitude and your objection to that form of punishment interfere with the way you deliberated upon the facts of the case?
A. No, it wouldn’t.
*376Q. You believe you can successfully set that aside and base your answers solely and exclusively upon the evidence you hear in the trial of the case?
A. Yes, Sir.
641 S.W.2d at 560.
. Ward was excused because he could not take the oath swearing that his decision would not be “affected” by the fact that the death penalty might be imposed. See Téx.Penal Code Ann. art. 12.31(b) (Vernon 1974).
. We have held, for example, that a trial court cannot exclude a juror who says that he or she would be able to serve as a juror but that he or she could not sign the verdict as the foreman. Alderman, supra, 663 F.2d at 563.
. Witherspoon holds that the state must establish that a juror’s automatic opposition to the death penalty is “unmistakably clear.” While a defendant who seeks to rehabilitate a juror might not be held to such an exacting standard, we express no view as to how certain a trial judge should be before he or she rejects the state’s challenge for cause on the basis of the defendant’s rehabilitation of the juror. We hold only that the defense counsel’s attempt at rehabilitation was insufficient here.
. There is ample support in the record of the first twenty pages of the voir dire for this position. For example:
THE COURT: From listening to the way you’ve explained your answers, I take it that you’re not necessarily opposed to it, but it would take an extreme set of circumstances for you to ever give it?
JUROR PFEFFER: That’s correct.
3 Trial Transcript at 875.
He * * * * *
THE COURT: Then, are you saying by virtue of that answer that you feel that there would be a set of circumstances that could exist whereby you as a member of a jury could feel that the death penalty would be a proper punishment and that you would return such a verdict if you felt it was proper?
JUROR PFEFFER: In general, I would say, and that was when I said with reservations. So, I still have reservations.
THE COURT: Well, everybody is going to have reservations. There’s no question about that. They’re just wanted to know how you feel personally as far as the death *380penalty being considered as punishment for crime. In other words, you apparently do not have any conscientious objection to the death penalty, do you?
JUROR PFEFFER: Not in general.
THE COURT: All right.
JUROR PFEFFER: But specific possibly.
THE COURT: And then, if you felt the facts and circumstances justified and warranted the death penalty being the verdict, could you join and vote with eleven others to return that verdict if you felt it was proper to do so under the facts and circumstances as you hear them from this witness stand?
JUROR PFEFFER: As I said, I don’t know. Like I say, I’m not set — I’m trying to answer your question.
THE COURT: I understand.
JUROR PFEFFER: But I know I’m vague; but I don’t trust myself on the judgment of this with — as you understand as you heard from my answers, I don’t have a concrete enough conviction either way. I just really—
THE COURT: Are you telling me then that this is just something that would be difficult within yourself to do, but you’re not necessarily opposed to it?
JUROR PFEFFER: I think this is correct.
THE COURT: And there may well be some facts and circumstances that do exist whereby you could and would, if you felt it was justified, return a verdict of death?
JUROR PFEFFER: Well, like I say, I still have the mixed feelings there that I don’t really think I could make a proper judgment, being a borderline thinker on the subject. I just don’t — a decision that I don’t know that I could make. Let’s put it that way.
THE COURT: Are you saying that under no circumstances could you ever make that decision or that it would just take an extreme set of circumstances before you would?
JUROR PFEFFER: It would take a very, very extreme set of circumstances to do it.
THE COURT: Then you’re not opposed to it. Is that correct?
JUROR PFEFFER: Well, I’m not opposed to it, but in my own heart I don’t know if I could make the decision, the proper decision with really by weighing the evidence, being on a thin line one way or the other. I mean, this is not directly — I know you would like direct answers, but this is the best I can do and it is a vague answer.
Id. at 879-82.
. Pfeffer may also be viewed as a person who is simply afraid to make a decision involving the death penalty, not because of scruples against the death penalty but because of concern about his ability to make a correct judgment on such an important matter. For example, Pfeffer explained to the trial court that he did not “trust [himself] on the judgment of this.” 3 Trial Transcript at 881. He continued: “I’m not opposed to it, but in my own heart I don’t know if I could make the decision, the proper decision with really by weighing the evidence.” Id. at 882. In view of the fact that the trial court excluded Pfeffer because he ultimately stated that he would automatically vote against the death penalty no matter what the trial revealed, we need not decide whether Witherspoon would permit exclusion of a juror who concludes that he would be unable to make a decision in a death penalty case.
. A portion of the voir dire was set forth in the majority opinion:
Q. Assuming that I prove the defendant committed first degree murder and is convicted, assume I prove the statutory requirements of aggravating circumstances, which under Louisiana law make the case appropriate for the death penalty, can you return a verdict that mandates that the defendant be put to death by electrocution?
A. (Ms. Brou) I don’t think I could do that.
Q. Okay. I appreciate your being honest with me. And let me ask you this. When you say I don’t think I can, what you are telling me, you can’t tell me positively that you can; is that correct?
A. (Ms. Brou) I know there is certain cases where you read about them and they are so hideous that you just think, oh, the death penalty would be the only good outcome, but this particular case, I don’t know.
Q. As the Judge told you, this is the killing of a — Well, I don’t know if the Judge said all that, but I think it is before the jury. This is the A & P robbery, murder that ■occurred on January the 5th of this year. And it is my understanding that you feel that you could not return the death penalty.
A. (Ms. Brou) Oh, let’s see. I’m afraid I couldn’t. I would just be thinking in terms of why can’t a person like that be rehabilitated rather than exterminated.
Q. So you feel that you could not return the death penalty?
A. (Ms. Brou) No.
Q. Are there any circumstances which you could return a verdict that would require a defendant to be electrocuted?
A. (Ms. Brou) This particular one or just in general?
Q. This particular one.
A. Any circumstances where I could do that?
Q. Yes.
A. (Ms. Brou) Well, of course, I don’t know that much about the case. I always think in terms of how hideous the crime is because I don’t know that much about it. I don’t know. I don’t think I can do it.
679 F.2d at 385 (emphasis in majority opinion). Immediately preceding this line of questioning, Ms. Brou asked whether a juror would be disqualified if she did not have a “firm conviction” about the death penalty. 679 F.2d at 399 n. 3 (Randall, J., dissenting).
. In Adams, supra, the Supreme Court stated that Witherspoon was not a ground for challenging any prospective juror, but rather a limitation on the state’s power to exclude jurors for cause. 448 U.S. at 47-48, 100 S.Ct. at 2527-28.
. The capital sentencing procedure is set forth in Tex.Code Crim.Pro.Ann. art. 37.071 (Vernon 1981), which provides in relevant part:
(a) Upon a finding that the defendant is guilty of a capital offense, the court shall conduct a separate sentencing proceeding to determine whether the defendant shall be sentenced to death or life imprisonment. The proceeding shall be conducted in the trial court before the trial jury as soon as practicable. In the proceeding, evidence may be presented as to any matter that the court deems relevant to sentence. This subsection shall not be construed to authorize the introduction of any evidence secured in violation of the Constitution of the United States or of the State of Texas. The state and the defendant or his counsel shall be permitted to present argument for or against sentence of death.
(b) On conclusion of the presentation of the evidence, the court shall submit the following issues to the jury:
(1) whether the conduct of the defendant that caused the death of the deceased was committed deliberately and with the reasonable expectation that the death of the deceased or another would result;
(2) whether there is a probability that the defendant would commit criminal acts of violence that would constitute a continuing threat to society;
(c) The state must prove each issue submitted beyond a reasonable doubt, and the jury shall return a special verdict of “yes” or “no” on each issue submitted.
(d) The court shall charge the jury that:
(1) it may not answer any issue “yes” unless it agrees unanimously; and
(2) it may not answer any issue “no” unless 10 or more jurors agree.
(e) If the jury returns an affirmative finding on each issue submitted under this article, the court shall sentence the defendant to death. If the jury returns a negative finding on any issue submitted under this article, the court shall sentence the defendant to confinement in the Texas Department of Corrections for life.
. O’Bryan did not object to the adequacy of the trial court’s instructions on mitigating circumstances until he filed his two applications for state habeas relief in 1980 and 1982. The Texas Court of Criminal Appeals denied both petitions without comment. O’Bryan did raise a more generalized challenge to the Texas capital sentencing procedure throughout the proceedings: that the procedure was unconstitu*384tional because it permitted the jury to make its decision in unbridled discretion and in an arbitrary and capricious manner. In its disposition of O’Bryan’s direct criminal appeal, the Texas Court of Criminal Appeals held: “Appellant’s contention that Article 37.071 is invalid under the United States Constitution has been answered adversely to him in Jurek v. Texas, 428 U.S. 262, 96 S.Ct. 2950, 49 L.Ed.2d 929 (1976). These two grounds of error are overruled.” O’Bryan v. State, 591 S.W.2d 464, 475 (Tex.Cr. App.1979) (en banc), cert. denied, 446 U.S. 988, 100 S.Ct. 2975, 64 L.Ed.2d 846 (1980). We agree with the Texas court that O’Bryan’s generalized claim that the Texas capital sentencing procedure is unconstitutional is foreclosed by the Supreme Court’s decision in Jurek.
. For example, O’Bryan has not demonstrated that the Texas courts have at times waived the procedural bar with respect to juror instructions because they were presented with a capital case. See Bell v. Watkins, 692 F.2d 999, 1004 n. 5 (5th Cir. 1982) (citing Culberson v. State, 379 So.2d 499 (Miss. 1980), cert. denied, 449 U.S. 1103, 101 S.Ct. 903, 66 L.Ed.2d 831 (1981)).
. In Engle, supra, the Supreme Court noted: [Tjhe futility of presenting an objection to the state courts cannot alone constitute cause for a failure to object at trial. If a defendant perceives a constitutional claim and believes it may find favor in the federal courts, he may not bypass the state courts simply because he thinks they will be unsympathetic to the claim.
Id. at 130, 102 S.Ct. at 1573. In Bass v. Estelle, 696 F.2d 1154 (5th Cir.), modified, 705 F.2d 121 (5th Cir.1983), the petitioner argued that the Texas courts apply a less exacting standard in deciding to excuse a procedural default where “a defect of constitutional magnitude has not been established at the time of trial,” quoting Cuevas v. State, 641 S.W.2d 558, 563 (Tex.Cr. App.1982) (en banc). We observed that some sort of objection to the exclusion of the jurors had been made in Cuevas, and that the quoted passage seemed “to apply only to situations where the grounds in question were novel and unknown.” 705 F.2d at 122. O’Bryan’s appellate brief, which relies on a Texas case dating from 1919 about the necessity of giving an instruction concerning the purpose of evidence of the defendant’s good reputation, Gilbert v. State, 84 Tex.Cr.R. 616, 209 S.W. 658, 659 (1919) (jury determination of suspended sentence), demonstrates that the ground of error urged here was not “novel and unknown.” Compare Bass, supra (contemporaneous objection rule applies where precise ground of objection — overbreadth of Texas oath requirement under Witherspoon — had been upheld year before trial) with Green v. Estelle, 706 F.2d 148 (5th Cir.), explained, 712 F.2d 995 (5th Cir. 1983) (federal court would not presume from state court’s silence that state court had applied procedural bar to claim of misuse of psychiatric testimony where petitioner’s trial was conducted before Supreme Court’s decision in Estelle v. Smith, 451 U.S. 454, 101 S.Ct. 1866, 68 L.Ed.2d 359 (1981)).
. Since O’Bryan has raised this claim throughout the proceedings and the Texas Court of Criminal Appeals reached the merits of the claim, we are not barred by Sykes, supra, from reviewing this variation on O’Bryan’s challenge to the constitutionality of his death sentence.
. Our standard for reviewing sufficiency of the evidence claims in collateral attacks upon state criminal proceedings is:
[T]he applicant is entitled to habeas corpus relief if it is found that upon the record evidence adduced at the trial no rational trier of fact could have found proof of guilt beyond a reasonable doubt.
Jackson v. Virginia, 443 U.S. 307, 324, 99 S.Ct. 2781, 2791, 61 L.Ed.2d 560 (1979) (sufficiency of evidence to support criminal conviction).
. The prosecutor stated:
People that know [the defendant] and know him well told you he is not worthy of belief under oath. He has a bad reputation for truth and veracity. You didn’t hear any of the witnesses that he called say anything about his reputation in the community for being a peaceful and a law abiding citizen, or for being a person of truth and veracity. No, and they weren’t asked that question by these defense lawyers because those witnesses would have told you the truth in that respect. They have a moral obligation if, in fact, this defendant has a good reputation in his community for being a peaceful citizen, a law abiding citizen, a citizen of truth, a citizen of veracity, to come in here and bring you those witnesses, and there are none.
14 Trial Transcript at 5276.
. Defense counsel mentioned the State’s failure to call any witnesses to testify about the probability of O’Bryan’s future dangerousness.
. O’Bryan has not alleged that the prosecutor’s comments violated any specific provision of the Bill of Rights.
. The court instructed the jury:
You are not to discuss among yourselves how long the defendant would be required to serve the sentence that you impose. Such matters come within the exclusive jurisdiction of the Board of Pardons and Paroles and the Governor and are no concern of yours.
14 Trial Transcript at 5254.