Child appeals from a judgment finding him to be within the jurisdiction of the court, for committing acts which, if committed by an adult, would constitute second degree sexual abuse. ORS 163.425.1 We review de novo and reverse.
Child, age 15, and the alleged victim, C., age 14, attended the same high school. Child dated C.’s best friend, Christina. One day after school, child and C. went for a walk in a wooded area near the high school. Child and C. give two different accounts of what happened in the woods.
According to C., child asked her to take a walk and, on the walk, asked if she wanted to have sex. She said no. Child threw her down “like a rag doll” and it hurt. She testified that the main thought running through her head was the knife that she had seen child carry in the past and that she was afraid he was going to take it out and cut her with it. Child knelt on C.’s feet and forcibly removed all of her clothes except for her sports bra. C. said “no” several times, but child had sexual intercourse with her as she lay on her back beneath child. During the entire sexual encounter, child continued to kneel on C.’s feet.
According to child, C. approached him and said that she needed to talk to him. He suggested that they go for a walk and, during the walk, she initiated the sexual encounter. He and C. had coats and sweaters, which they spread on the ground. C. was on top during the encounter, which was consensual.
Some of the events during and after the sexual encounter are undisputed. No knife or other weapon was mentioned or displayed by child at any time during the encounter. Following the encounter, child and C. both testified that they walked back to the high school together and stopped in an orchard for a cigarette. C. testified that child did *316not force her to accompany him. They went to a car so that child could retrieve an item he needed, then entered the high school together and phoned Christina to tell her about the sexual encounter. C. testified that she was positive that she placed the call, using her own quarter. However, child and Christina testified that child placed the call. Child testified that he told Christina that she would be mad at him, but he could not tell her that he and C. had had sex. Both child and C. testified that it was C. who told Christina that they had had sex. Child testified that he felt guilty about the encounter and told C. so C. testified that she told Christina about the sexual encounter “because [she] was afraid for [Christina’s] safety,” but she did not tell Christina that child had raped her, because she was afraid child would “come after her [C.].” Drew, a school administrator, saw child and C. around the time of the phone call. Drew testified that child and C. behaved “like two people that seemed as if nothing had happened.”
C. then rode the bus home. On the bus, she told a friend, Melinda, about the encounter. C. testified about her conversation with Melinda:
“I didn’t go into details with her, but I — I had to tell somebody because I was bursting with anger and I was frustrated and I didn’t know what to make of what happened yet. And I told her that I had sex willingly with [child].”
C. also testified that she discussed the sexual encounter with her father that evening:
“A: Yeah, I told my dad that I had mutual sex.
“Q: Okay. Why did you tell your dad?
‘ ‘A: Because me and my dad have a really good relationship and I tell him everything.
“Q: But you didn’t tell him you’d been raped?
“A: No, ’cause I — I was scared and I was embarrassed and I wasn’t quite sure what to make of it yet, again, and I — they didn’t really do nothing. I just — I was crying like crazy ’cause I wanted to tell them.”
C. also testified that the evening of the alleged rape, Christina phoned C. and called her “a bunch of names.”
*317The day after the sexual encounter with child, C. told the school counselor that she had been raped. The counselor called the police. Wampler, one of the officers who interviewed C., testified that C. stated that she ended up on the ground because she tripped on a root and fell backwards and that child, not C., called Christina. At the time of the interview, C. appeared to be embarrassed and scared. Tubbs, the other officer who interviewed C., testified that C. said that child had called Christina and that C. made no reference to thinking about a knife when she described the sexual encounter.
Dr. Pendleton, who was C.’s pediatrician, examined C. the day after the alleged rape. He testified that he found some trauma to her perineum, but no bruising or scratches anywhere else on her body. Pendleton testified that the level of trauma he discovered in his exam could be the result of either consensual or non-consensual sex:
“Q. Okay. Well, I think you testified that it’s possible to avoid these injuries [to the perineum], but intercourse must be — and I — these are your — your words — very, very slow. Is that right?
“A. Penetration must be very, very slow.
“Q. Okay. Alright.
“A. Very, very slow.
“Q. Okay.”
Pendleton testified that even an aggressive pelvic exam could inflict the same trauma, and he was equivocal when asked if the extent of injuries was consistent with non-consensual sex:
“A. Getting back to the — to the issue of the emotional trauma, it’s not at all unusual for individuals to be — be raped, for women to he raped and not have any injury other than what’s to their perineum.
“Q. Not unusual, but not common either, is it?
“A. I don’t know how to answer that. It’s — it—you know, it — You see it, and I can’t give you a percentage. Probably — I just — and I — I couldn’t speculate.”
The juvenile department filed a petition alleging that child was within the jurisdiction of the court, because he committed an act which, if done by an adult, would constitute *318first degree rape. ORS 163.375. The petition was later amended to add an allegation that the act, if committed by an adult, would constitute second degree sexual abuse. ORS 163.425. Pendleton, Wampler, Tubbs, Drew, Christina, C., C.’s therapist, child, two employees of the juvenile department and several teenage witnesses appeared and testified at the hearing.
Several of the teenage witnesses testified, without objection, that C. had accused another teenage boy of rape approximately two weeks before the alleged rape by child. They also testified that C. had a poor reputation for truthfulness. Drew and the juvenile department employees testified that child and many of the teenage witnesses (excluding C.) had poor reputations for truthfulness.
The state offered the testimony of C.’s therapist to explain inconsistencies in C.’s account of the alleged rape. The therapist theorized that C. was traumatized by the encounter and that the reason she told her father and friends that the encounter was consensual was that she was “trying to understand what happened to her.” According to the therapist, victims of trauma are frequently confused:
“A: [A]fter what has happened and her hrain has become disorganized during the trauma, she may not make a lot of sense the next days or weeks even. She may not interpret what happened to her in a way that uses logic or that we would understand.
<<* * * Hí H:
“Q: And it’s always possible that she may not be — he able to relate all the details of the event because they simply didn’t happen that way?
* * * *
“A: I don’t have great experience working with people who make up stories or lie about these things, so I really can’t answer that.”
The trial court found that the sexual encounter was non-consensual but did not find that there was forcible compulsion. As a result, the court found child to be within the jurisdiction of the juvenile court on the charge of sexual abuse in the second degree and dismissed the charge of rape in the first degree. The court stated that it relied primarily on the *319testimony of child, Pendleton and C. The court did not make express credibility findings of witnesses who testified on key issues.2 However, based on the result that it reached, the trial court must have rejected some portions of C.’s account of the alleged rape. The trial court’s result also implies that it rejected all or part of child’s testimony.
We review de novo. ORS 419A.200(5). The facts alleged in the petition showing that child committed second degree sexual abuse must be established beyond a reasonable doubt. ORS 419C.400(2). We give deference to the trial court’s credibility findings. State ex rel Juv. Dept. v. Greenwood, 107 Or App 678, 680-81, 813 P2d 58 (1991). The degree of deference we give varies with the importance of the trial court’s opportunity to observe the witnesses, Brunswick v. Rundell, 126 Or App 582, 586, 869 P2d 886 (1994), and our ability to discern the trial court’s specific credibility determination. In a rape or sexual abuse case, the trial court’s opportunity to observe the demeanor of the defendant and the complainant is important. However, demeanor is not the only measure of credibility; internal consistency, logic, and corroboration also guide us. To the extent that a credibility determination is based on a comparison of the witness’ testimony with the substance of other evidence, this court is as well equipped as the trial court to make that credibility determination. In re Schenck, 318 Or 402, 420, 870 P2d 185 (1994).
C.’s testimony was internally inconsistent and conflicted with much of the other evidence in this case. We first note major discrepancies between what C. told law enforcement officers and what she said at the hearing. C. never mentioned child’s knife to the school counselor, Tubbs, Wampler or any other person investigating the incident. However, at trial, she testified:
“Q. * * * So I guess when this was happening, that.. . that knife was really the main thing you were thinking of, huh?
“A. Yeah, and to stay alive.
*320“Q. He was afraid — you were afraid he was going to take you ... take it out and cut you with it?
“A. Yeah.”
It seems inconceivable that C. never mentioned the object that caused her to fear for her life to the people investigating this incident. In addition, when C. was interviewed by Wam-pler, she told him that she ended up on the ground when she tripped over a root. At the hearing, she testified that child threw her down like “a rag doll.” C. also testified that child had his knees on her feet throughout the rape. The near impossibility of such a feat, coupled with the fact that there was no bruising anywhere on C.’s lower legs or feet, calls.into question her version of the incident.
Perhaps most troubling is the fact that she voluntarily told three different people that she had had consensual sex with child. One of the people she told was Christina, her best friend and child’s then girlfriend. C. testified that she called Christina because she was “concerned for her safety,” that child had raped her and might do the same to Christina. However, she made this phone call with child, the very person she was concerned would harm Christina, standing next to her. Substantial portions of C.’s testimony are internally inconsistent, incoherent and not credible.
These inconsistencies are not reconciled by the physical and medical evidence. Although C. testified that she was raped after being pushed, falling hard and being held down virtually naked on the ground in a wooded area, the physical examination the next day revealed no scratches or bruises on her back, legs, or buttocks.3 Moreover, although the state points to the trauma to C.’s perineum as corroborating her testimony, any corroboration was equivocal. Pendleton testified that such trauma could be consistent with either the sort of assault C. described or consensual sex that was not “very, very slow.”
Finally, the testimony of C.’s therapist is inadequate to repair the material inconsistencies in C.’s account and the consequent lack of credibility. The therapist testified that complainants in rape cases generally change their accounts of *321events in an effort to “understand what happened to them” and that all variations of C.’s testimony resulted from trauma. We recognize that trauma can commonly interfere with a victim’s ability to recall events. However, the therapist’s testimony here is reduced to the proposition that any statements by the alleged victim, no matter how incredible or how inconsistent, are to be discounted as the product of post-traumatic stress. Thus, in the therapist’s view, a description of a sexual encounter as being consensual is just as consistent with rape as the obverse. Viewed de novo on this record, such testimony is insufficient, without other, objective corroboration, to explain the inconsistencies in C.’s account.
We are very troubled by this case; however, because proof of guilt must be beyond a reasonable doubt, we believe no other result is possible. The dissent calls this “a classic case of ‘his word against hers.’ ” This is not a classic case, because, in this case, both his word and her word are highly questionable in material particulars. We cannot say on de novo review that there is no reasonable doubt when the only two witnesses give diametrically opposed accounts, both of which are highly questionable, the medical evidence is only slightly better than equivocal and there is no other corroboration in the record. In sum, the evidence in the case does not show, beyond a reasonable doubt, that child committed acts which, if done by an adult, would constitute sexual abuse in the second degree. We reverse the judgment finding him to be within the jurisdiction of the court.
Reversed.
ORS 163.425(1) provides:
“A person commits the crime of sexual abuse in the second degree when that person subjects another person to sexual intercourse, deviate sexual intercourse or, except as provided in ORS 163.412, penetration of the vagina, anus or penis with any object other than the penis or mouth of the actor and the victim does not consent thereto.”
The court found one of child’s witnesses not credible, but her testimony is unnecessary to our holding.
C. testified that she did not bruise easily.