What is the test for sufficiency of evidence to support a rape conviction?

When the trier of fact relies on inferences, "those inferences must be reasonable. An inference is not reasonable if it is based only on speculation." (People v. Holt (1997) 15 Cal.4th 619, 669.) The defendant in Holt challenged the sufficiency of the evidence to support a rape conviction. The evidence showed some sort of unlawful sexual conduct had occurred, as shown by semen on both the defendant and the victim, but the laboratory analysis of the victim, whom defendant had killed, showed no traumatic evidence of penetration and no semen in the vagina or anus. (Id. at p. 668.) The evidence also showed redness in the vaginal area, which was consistent with either sexual intercourse or an infection. The defendant suggested that the evidence that an infection could have caused the redness, coupled with the finding of apparent blood in the anus, suggested that any sexual assault involved sodomy, not rape. (Ibid.) Our high court rejected this contention, reasoning, "That the evidence might lead to a different verdict does not warrant a conclusion that the evidence supporting the verdict is insubstantial. [Citation.]" (Id. at p. 669.)