A woman can rape a man by having sex with him without his consent, such as when he is drunk, stoned, and/or asleep. His body will respond to physical stimulus, even though he may not be aware of it.
Being that there are now laws that say that not being able to giving consent for sex (due to unconsciousness, for example) is the same as saying "No", a man who has sex with an unconscious woman is committing rape.
Unfortunately, the common myth is that men always want sex, and would never pass up the chance to have sex even in their sleep.
If you think that no one would believe a woman when she says she's been raped, try to imagine a man explaining why (1) he did not want to have sex, and (2) why he did not want to have sex with a woman - especially a pretty woman.
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The mere fact that science may not yet adequately explain an object, event, or experience does not mean the immediate explanation should automatically default to a conspiratorial, extraterrestrial, paranormal, or supernatural cause.