This is a review of an unpublished decision of the court of appeals which reversed both the judgment of conviction for first-degree sexual assault entered by the circuit court for Milwaukee county, the Honorable Michael D. Guolee, Judge, and the order denying the defendant’s motion for a new trial entered by the Honorable Ralph Adam Fine, Judge. The issue on appeal is whether the defendant was denied his right to a unanimous jury verdict.
On November 3, 1980, the defendant, Charles Joseph Lomagro, and Chester L. Cyrus were each charged with one count of first-degree sexual assault, party to a crime, in violation of secs. 940.225(1) (c)1 and 939.05, Stats. The testimony of the victim, C.G., and the defendant Lomagro at the trial as to the facts surrounding the incident was in substantial dispute.
C.G. testified that on the evening of October 31, 1980, she arrived with two friends at a bar on Milwaukee’s south side at approximately 11:15 p.m. While at the bar she met the defendant and Cyrus and talked to the two men for most of the evening.
Shortly after midnight C.G. noticed that her two friends had left the bar without her. Cyrus and the defendant then offered C.G. a ride to meet her friends at the restaurant where she worked. C.G. hesitated, but accepted the ride when the owner of the bar assured her that she knew the defendant and that he would get her home safely. C.G. left the bar with the two men at approximately 12:30 or 12:45 a.m., and the three entered Cyrus’s station wagon. All three sat in the front seat *584with C.G. in the middle between Cyrus, who was driving, and Lomagro who sat on the right passenger side.
Soon after they drove away C.G. agreed to accompany the two men to an east side bar. When she noticed that they were at the lakefront and had gone farther than their destination, she questioned the two men as to what was going on. The defendant responded by reaching down the front of C.G.’s dress and grabbing her breast. C.G. begged him to stop. The defendant told her to be quiet or he would blow her brains out with his gun. While the car proceeded along the lakefront, both men ripped the crotch area of C.G.’s jumpsuit and removed her pantyhose.
The defendant then forced C.G. to engage in an act of penis-vagina intercourse. They continued to drive and a short time later the defendant forced her to engage in another act of penis-vagina intercourse. During this second assault, C.G. attempted three times to throw open the passenger door. The defendant responded by slapping C.G.’s face, biting her nose and shoving her back in the car.
Cyrus then drove the car to an industrial area where he forced C.G. to engage in an act of penis-vagina intercourse. After leaving the area and while they were driving, Cyrus forced C.G. to perform an act of fellatio on him. Cyrus then drove the car to a gas station. While Cyrus put gas in the car, C.G. remained in the car with the defendant.
Upon leaving the gas station they proceeded to another secluded area and C.G. was forced to perform an act of fellatio on both men. The two men then agreed to release her. At about 3:00 a.m., she was taken to a friend’s home.
The defendant acknowledged meeting C.G. at the south side bar and offering her a ride. His version of the subsequent events, however, was substantially dif*585ferent. He testified that they left the bar at approximately 1:00 a.m. and agreed to go to the east side bar. When they arrived at the bar, they decided not to stop because it appeared that the bar was emptying out. They then proceeded to take C.G. home, stopping only to get some gas. The defendant stated that they dropped C.G. off unharmed at her home between 2:00 and 2:15 a.m. He testified that neither he nor Cyrus had any sexual contact with C.G. and that neither man ever struck her.
Photographs of C.G. taken several days after the incident showed a variety of scratch marks and bruises. The jumpsuit worn by the victim was marked as an exhibit at trial and contained numerous holes with the whole crotch area ripped out. There was additional testimony by an employee of the State Crime Laboratory. He testified that there was sperm found on the victim’s clothing and on her cervical and vaginal smears, but that her oral smears and swabs were negative.
Following the close of the evidence, the trial court instructed the jury on the elements of first-degree sexual assault, party to a crime. The court told the jury that both penis penetration into the vagina and fellatio constituted the element of sexual intercourse. The court gave the standard unanimity instruction as follows:
“This is a criminal, not a civil, case. Therefore, before the jury can return a verdict that can legally be received, your verdict must be reached unanimously. In a criminal case all twelve jurors must agree in order to arrive at a verdict.”
The jury returned its verdict finding the defendant guilty of first-degree sexual assault. Following sentencing, the defendant filed a motion requesting a new trial on the grounds that his rights to due process and a unanimous verdict were violated. He contended that when the state presents evidence of separate crimes and charges only one count, the jury must agree as to the specific act that constituted the crime.
*586The trial court rejected this argument, finding that fellatio and penis-vagina intercourse were merely alternative ways of committing first-degree sexual assault and that jury unanimity was not required as to the different ways of committing a single criminal act. The court of appeals reversed, holding that the defendant’s rights to due process and a unanimous verdict were violated. The court reasoned that in order to protect the defendant’s right to a unanimous verdict when separate crimes are joined in one count, the jury must be instructed that it must unanimously agree that defendant committed one specific act of sexual intercourse. We granted the state’s petition to review.
This review raises the issue of whether the defendant’s right to a unanimous verdict was violated when he was charged with one count of first-degree sexual assault, but evidence was introduced of six different acts of non-consensual sexual intercourse. In order to resolve this issue, we first must determine whether the state may join several distinct acts of sexual intercourse into one count. The defendant contends that because the sexual assault charged in this matter consisted of six separately chargeable offenses, combining them in one count is duplicitous. The state argues that the prosecutor has the option to charge separate or multiple offenses when the separate acts are committed by the same person at substantially the same time.
Duplicity is the joining in a single count of two or more separate offenses. State v. George, 69 Wis. 2d 92, 99, 230 N.W.2d 253 (1975) ; Harrell v. State, 88 Wis. 2d 546, 555, 277 N.W.2d 462 (Ct. App. 1979). The purposes of the prohibition against duplicity are: (1) to assure that the defendant is sufficiently notified of the charge; (2) to protect the defendant against double jeopardy; (3) to avoid prejudice and confusion arising from evi-*587dentiary rulings during trial; (4) to assure that the defendant is appropriately sentenced for the crime charged; and (5) to guarantee jury unanimity. United States v. Alsobrook, 620 F.2d 139, 142 (6th Cir. 1980), cert. denied 449 U.S. 843 (1980) ; United States v. Pavloski, 574 F.2d 933, 936 (7th Cir. 1978); United States v. Starks, 515 F.2d 112, 116-17 (3d Cir. 1975).
The first step in determining whether a criminal complaint is duplicitous is to examine its factual allegations to determine whether it states more than one offense. The complaint involved here alleged that the two co-defendants forced C.G. to engage in three acts of sexual intercourse.2 The complaint characterizes the actions of the co-defendants in committing these sexual assaults as one continuous course of conduct resulting in one charge of first-degree sexual assault.
This court has consistently held that acts which alone constitute separately chargeable offenses, “when committed by the same person at substantially the same time and relating to one continued transaction, may be coupled in one count as constituting but one offense” without violating the rule against duplicity. Huotte v. State, 164 Wis. 354, 356, 160 N.W. 64 (1916); Blenski v. State, 73 Wis. 2d 685, 695, 245 N.W.2d 906 (1976). If the defendant’s actions in committing the separate offenses may properly be viewed as one continuing offense, it is within the state’s discretion to elect whether to charge “one continuous offense or a single offense or series of single offenses.” State v. George, 69 Wis. 2d at 100. See also, State v. Copening, 103 Wis. 2d 564, 572, 309 N.W.2d 850 (Ct. App. 1981). This rule has been *588applied in other states to sex offenses. See e.g., Steele v. State, 523 S.W.2d 685, 686-87 (Tex. Cr. 1975).
However, this prosecutorial discretion to join separately chargeable offenses into one count is not unlimited. Rather, this discretion to join offenses is limited by the purposes of the prohibition against duplicity as discussed above. As stated by the Sixth Circuit in United States v. Alsobrook, 620 F.2d at 142-43:
“Several courts have upheld the validity of indictments that consolidate several acts into a single count when such acts represent a single, continuing scheme that occurred within a short period of time and that involved the same defendant. See United States v. Girard, 601 F.2d 69 (2nd Cir. 1979) ; United States v. Pavloski, 574 F.2d 933 (7th Cir. 1978) ; Cohen v. United States, 378 F.2d 751 (9th Cir.), cert. denied, 389 U.S. 897, 88 S. Ct. 217, 19 L. Ed. 2d 215 (1967). The determination of whether a group of acts represents a single, continuing scheme or a set of separate and distinct offenses is a difficult one that must be left at least initially to the discretion of the prosecution. This discretion, however, is not without limits. See e.g., United States v. Tanner, 471 F.2d 128 (7th Cir. 1972). Ultimately, the indictment must be measured in terms of whether it exposes the defendant to any of the inherent dangers of a duplicitous indictment. See United States v. Pavloski, supra. Those dangers include the possibility that the defendant may not be properly notified of the charges against him, that he may be subjected to double jeopardy, that he may be prejudiced by evidentiary rulings during the trial, and that he may be convicted by a less than unanimous verdict. If any of these dangers are present, the acts of the defendant should be separated into different counts even though they may represent a single, continuing scheme.
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“. . . We find it difficult to criticize the government’s exercise of discretion when it redounds to the benefit of the defendant as it did in this case. More importantly, however, we are hesitant to create an inflexible rule that would force the government to charge each punish*589able act as a separate count and thereby to cumulate both offenses and possible punishments.”
We also adopt this flexible rule that it is initially up to the state to determine the appropriate charging unit for a particular criminal episode. When separate criminal offenses of the same type occur during one continuous criminal transaction, the prosecutor may join these acts in a single count if they can properly be viewed as one continuous occurrence without violating the protections afforded the defendant by the rule against duplicity. The prosecutor must have this discretion at the charging stage to issue charges which coincide with the evidence available and the gravity of the particular course of conduct involved.
If a complaint joins several criminal acts which can properly be characterized as a continuing offense in one count and is challenged by the defendant on grounds of duplicity, the trial court must examine the allegations in light of the purposes of the prohibition against duplicity. Such a complaint may be found to be duplicitous only if any of these dangers are present and cannot be cured by instructions to the jury. If the complaint is found to be duplicitous, the state must then either elect the act upon which it will rely or separate the acts into separate counts.
Applying this analysis to the instant case, we find that the complaint was not duplicitous The acts alleged in the complaint were committed by the same two co-defendants in a short period of time and as part of one continuous criminal transaction. We believe that it was proper for the state to charge the defendant with one offense.
The defendant’s only objection to the complaint on grounds of duplicity is that it violated his right to a *590unanimous verdict.3 This brings us to the underlying issue of this case. If the prosecutor issues only one charge but introduces evidence of multiple acts which separately constitute the criminal offense charged, must the jurors unanimously agree as to which act or acts the defendant committed in order to find the defendant guilty?
This court has long held that the right to a jury trial as guaranteed by the Wisconsin Constitution4 includes the right to a unanimous verdict. Holland v. State, 91 Wis. 2d 134, 138, 280 N.W.2d 288 (1979), cert. denied, 445 U.S. 931 (1980) ; Vogel v. State, 138 Wis. 315, 332-33, 119 N.W. 190 (1909) ; Boldt v. State, 72 Wis. 7, 14-16, *59138 N.W. 177 (1888). The principal justification for the unanimity requirement is that it ensures that each juror is convinced beyond a reasonable doubt that the prosecution has proved each essential element of the offense. Commentators have viewed the requirement as one that compels jurors to carefully examine the evidence presented in order to reach a consensus. Notes, Constitw-tional Law — Criminal Procedure — Jury Instructions and the Unanimous Jury Verdict, 1978 Wis. L. Rev. 339, 349. While it is clear that a unanimous verdict is required, “substantial doubt exists as to what the jury has to be unanimous about.” Manson v. State, 101 Wis. 2d 413, 433, 304 N.W.2d 729 (1981) (Abrahamson, J. concurring) .
Any discussion regarding unanimity must begin with a consideration of United States v. Gipson, 553 F.2d 453 (5th Cir. 1977). It is the leading case on the requirement of jury unanimity, and this court has adopted its analysis when deciding jury unanimity issues. Manson, 101 Wis. 2d at 429, n. 6.
Gipson was convicted of violating 18 U.S.C. sec. 2313. That statute imposes criminal liability on one who “receives, conceals, stores, barters, sells or disposes of” a stolen vehicle in interstate commerce. In response to a jury request for additional instructions, the judge charged the jury that it could find the defendant guilty without unanimously agreeing on which of the six acts prohibited by the statute he had committed. The jury returned a guilty verdict.
The Court of Appeals for the Fifth Circuit reversed the conviction. The court reasoned that where a statute can be violated by different acts, a “prerequisite of jury consensus as to the defendant’s course of action” is required to ensure a unanimous verdict. Gipson, 553 F.2d at 458. After examining the statute, the court noted that *592the six prohibited acts fell into two distinct conceptual groupings. The conceptual group of “receiving, concealing, and storing” was viewed as a “housing” actus reus.5 The other group of “bartering, selling, and disposing” was viewed as a “marketing” actus reus. The court reasoned that acts within each group were “sufficiently analogous” to each other so that the jury did not have to agree on which of the intragroup acts the defendants committed in order to achieve a unanimous verdict. Since some jurors may have believed that Gip-son “housed” a stolen vehicle and others that he “marketed” a stolen vehicle, the court concluded that he was denied a unanimous verdict and deserved a new trial.
In Manson v. State, 101 Wis.2d 413, this court following the logic of Gipson, adopted the following analysis for determining whether a defendant’s right to a unanimous jury verdict has been denied. The first step is to determine whether the jury has been presented with evidence of multiple crimes or evidence of alternate means of committing the actus reus element of one crime. If more than one crime is presented to the jury, unanimity is required as to each. Id. at 419. If there is only one crime, jury unanimity on the particular alternative means of committing the crime is required only if the acts are conceptually distinct. Unanimity is not required if the acts are conceptually similar. Id. at 419, 428-30.
This defendant was charged with one crime of first-degree sexual assault. The evidence of the acts of non-consensual sexual intercourse constitutes alternative means of committing that crime. The next step under Manson then is to determine whether the six acts of sexual intercourse were conceptually similar.
*593Sexual intercourse is defined for purposes of the sexual assault statutes in sec. 940.225(5) (b), Stats. That section states:
“(b) ‘Sexual intercourse’ includes the meaning assigned under s. 939.22(36) as well as cunnilingus, fellatio or anal intercourse between persons or any other intrusion, however slight, of any part of a person’s body or of any object into the genital or anal opening either by the defendant or upon the defendant’s instruction. The emission of semen is not required.”
By reference vulvar penetration (sec. 939.22(36)) is included in sec. 940.225(5) (b) and, therefore, both forms of the defendant’s behavior, penis-mouth and penis-vulvar penetration, are sexual intercourse.
In State v. Baldwin, 101 Wis. 2d 441, 450, 304 N.W.2d 742 (1981), this court stated that the “proper application of the Gipson rationale is not dependent upon the conceptual dissimilarity, but rather the conceptual similarity of the conduct.” The multiple acts of penis-vagina intercourse and fellatio that occurred during the one continuous carnal invasion of the victim’s body are conceptually similar. The acts all involve the penetration of an orifice of the victim’s body.
We recognize that a reasonable person could believe that penis-vagina intercourse and fellatio are conceptually distinct, since the acts involve different orifices of the victim. However, in our view, such an argument has been foreclosed by the legislature. By specifically defining what acts constitute sexual intercourse in sec. 940.225(5) (b), Stats., the legislature has in effect performed the conceptual grouping as a matter of public policy. By grouping the acts together under one definition, the legislature chose not to distinguish between the cruelty and effect caused by the acts on a victim and has already determined that the acts are conceptually similar.
*594Recently in State v. Giwosky, 109 Wis. 2d 446, 326 N.W.2d 232 (1982), we considered the issue of jury unanimity as applied to battery. In Giwosky, the defendant was charged with one count. At trial, evidence was presented that demonstrated that the victim was injured as a result of a thrown log and then punches and kicks during a fight with the defendant. The court observed that the encounter lasted only a few minutes with no “break in the action” and concluded that it was proper for the jury to consider the incident as one continuous event.
In Giwosky, we held:
“[T]he unanimity requirement was satisfied by the instruction that the jurors must agree that the defendant intentionally committed an act which caused bodily harm to the defendant [victim]. The defendant’s actions during the brief encounter are not practically or legally separable or distinct.” Id, at 458.
The rationale of Giwosky is applicable to this case. The fact that the encounter in this case lasted two hours and only a few minutes in Giwosky is not legally significant. Both encounters were one continuous, unlawful event and chargeable as one count. The Giwosky jury was not required to unanimously agree which blow by the defendant caused injury to the victim because the court concluded that there was no conceptual distinction between the throwing of the log and punches and kicks. Unanimity was achieved “[a]s long as the jury agreed that the defendant intentionally committed an act which caused physical harm.” Id. at 458. There is no more of a conceptual distinction between being injured by a thrown log, a punch or a kick, than being sexually assaulted by penetration into different orifices. In this case unanimity was achieved, since the jury agreed that a sexual assault was committed.
*595The instruction given in the instant case, which was similar to the one given in GiwosJcy, was sufficient to assure a unanimous verdict. The relevant parts of the instructions were:
“The first element requires that the defendant had sexual intercourse with [C.G.]. Sexual intercourse means any penetration by the penis of a male into the genital organs of a female. If there is any such penetration, no matter how slight, then there is sexual intercourse, and it is immaterial whether the sexual act proceeded any further. Sexual intercourse requires only vulvar penetration and does not require emission. There must be some penetration to constitute the crime, but a very slight actual penetration is sufficient; the engagement of the sexual organs at all, beyond surface contact, is sexual intercourse. Sexual intercourse includes fallatio [sic]. Fallatio [sic] is oral stimulation of the penis. Emission is not required.
“This is a criminal, not a civil, case. Therefore, before the jury can return a verdict that can legally be received, your verdict must be reached unanimously. In a criminal case all twelve jurors must agree in order to arrive at a verdict.”
We hold the instructions given under the facts of this case sufficient for the jury to return a unanimous verdict that the defendant was guilty of violating sec. 940.-225(1) (c), Stats. The critical facts in this case are that the defendant testified that neither he nor the co-defendant engaged in any sexual acts with the victim, while the victim testified that the defendant performed three sexual assaults and aided and abetted three other assaults within the confines of a car over a two-hour period. The jury chose to believe the victim making it unnecessary for it to be unanimous about each specific act. As we stated in Holland v. State, 91 Wis. 2d 134, 143: “Unanimity is required only with respect to the *596ultimate issue of the defendant’s guilt or innocence of the crime charged.”
The defendant contends that Boldt v. State, 72 Wis. 7, and Vogel v. State, 138 Wis. 315, stand for the proposition that the jury must unanimously agree upon a specific criminal act when the state submits evidence of multiple criminal acts in support of a single criminal charge. Both cases are distinguishable from this case.
In Boldt, the defendant was charged with one count of unlawfully selling liquor. At trial, the state introduced evidence showing that the defendant sold liquor without a license to a variety of different people on different days. This court reversed the conviction because of potential jury unanimity problems. The distinction between this case and Boldt is that the crime in Boldt cannot be viewed as a single, continuous criminal transaction as can a sexual assault that is committed on the same victim in a two-hour period.
In Vogel, five defendants were jointly charged as parties to a crime with one count of rape. The victim alleged that she was raped 22 times during a two-hour time period. The unanimity issue in Vogel concerned the proper application of the aiding and abetting law as it existed at that time. There was evidence introduced to the jury showing that not all of the defendants may have been present during all 22 acts. In order to find all five defendants guilty as parties to the crime, the court required the jury to agree “upon some act at which it believed all the defendants were present.” Id. at 334. The court did not state that there had to be unanimity as to one of the several acts of sexual intercourse that took place while all of the defendants were present, only that an act of rape occurred while all were present.
The defendant also argues that this court’s decision in State v. Eisch, 96 Wis. 2d 25, 291 N.W.2d 800 (1980), *597compels the reversal of his conviction. In Eiseh, we held that it was not multiplicitous to charge a defendant with four counts of second-degree sexual assault for four different kinds of sexual intercourse that the defendant forced the victim to perform over a two-hour period. The defendant in Eisch had been charged with genital intercourse, anal intercourse, fellatio and inserting a beer bottle into the victim’s genitals. Each of the alleged acts of intercourse was accompanied by separate threats and distinct uses of force. The court concluded that since each act involved a “significantly different” intrusion, it was proper to charge separately.
The defendant maintains that since penis-vagina intercourse and fellatio are separate and distinct crimes which could be separately charged although arising out of one continuous sexual assault, it follows that the acts are conceptually distinct for purposes of the Gipson-Manson analysis. That is not necessarily true. Simply because the Eiseh court found the different forms of penetration as a controlling factor when determining if a charge is multiplicitous, does not necessarily mean that those same acts cannot be deemed conceptually similar for purposes of jury unanimity issues.6
*598The defendant also relies on a footnote in Eisch which stated: “In passing, we note our agreement with the state’s ancillary argument that submission of proof of the four separate offenses in support of a single count may well deprive the defendant of the right to a unanimous jury verdict.” Id. at 42, n. 6. That statement was dicta, since the unanimity issue was not before the Eisch court.
In conclusion, we hold that the sexual assault in this case can be characterized as one continuing criminal episode and properly chargeable as one offense. Under these circumstances, even though evidence of different acts was introduced at trial, the jury did not have to be unanimous as to which specific act the defendant committed in order to convict the defendant, since the acts were conceptually similar.
By the Court. — The decision of the court of appeals is reversed.
See. 940.225(1) (c), Stats., provides:
“940.225 Sexual assault. (1) First degree sexual assault. Whoever does any of the following is guilty of a Class B felony:
“(c) Is aided or abetted by one or more other persons and has sexual contact or sexual intercourse with another person without consent of that person by use or threat of force or violence.”
The complaint alleged that C.G. was forced to engage in one act of penis-vagina intercourse and one act of fellatio with Loma-gro and one act of fellatio with Cyrus.
At oral argument counsel for the defendant stated that none of the other dangers potentially arising from a duplicitous complaint were present in this case.
The defendant never raised the issue of duplicitous charging until he was before this court in this review. Such an objection is waived if not raised before the trial court. Lampkins v. State, 51 Wis. 2d 564, 570, 187 N.W.2d 164 (1971); sec. 971.31(2), Stats. However, we have discussed this issue because of its interrelation to the issue of the defendant’s right to a unanimous verdict.
Art. I, secs. 5 and 7 of the Wisconsin Constitution provide:
“Trial by jury; verdict in civil cases. Section 5. [As amended, Nov. 1922] The right of trial by jury shall remain inviolate, and shall extend to all cases at law without regard to the amount in controversy; but a jury trial may be waived by the parties in all cases in the manner prescribed by law. Provided, however, that the legislature may, from time to time, by statute provide that a valid verdict, in civil cases, may be based on the votes of a specified number of the jury, not less than five-sixths thereof.”
“Rights of accused. Section 7. In all criminal prosecutions the accused shall enjoy the right to be heard by himself and counsel; to demand the nature and cause of the accusation against him; to meet the witnesses face to face; to have compulsory process to compel the attendance of witnesses in his behalf; and in prosecutions by indictment, or information, to a speedy public trial by an impartial jury of the county or district wherein the offense shall have been committed; which county or district shall have been previously ascertained by law.”
Actus reus denotes such result of human conduct as the law seeks to prevent. See generally J. Hall, General Principles of Criminal Law (2d ed. 1960).
What does follow from Eisch is that in the instant case, it would have been within the state’s discretion to charge the defendant with six offenses. To determine whether different acts of bodily intrusion are chargeable separately, the prosecutor must carefully examine the evidence that is available. The factors to consider include the types of acts of penetration, the time intervals between penetrations, the behavior of the defendant between penetrations, changes in geographical location, and any other facts concerning the surrounding conditions under which the assault took place. See Harrell v. State, 88 Wis. 2d 546, 672-74, 277 N.W.2d 462 (Ct. App. 1979). The record in this case demonstrates that it would have been proper to charge the defendant for each of the sexual acts. But as discussed earlier in this opinion, since the assault could also be viewed as one continuing criminal episode, the. state did not have to charge separately.