One thing I've always wondered about these experiments: why do we assume humans can't (perhaps subconsciously) tell that the person in pain is faking?

I remember a friend describing hearing a woman attacked on her college campus. She said the screams the woman made were like nothing she has heard before or since, they were incredibly disturbing and unmistakably the sound of someone in terror and pain. I have also never listened to the audio recording of the "grizzly man" and his girlfriend being attacked by a bear, but have heard it is so horrible, you can never "un-hear" it.

Isn't it possible the faked pain just doesn't trigger a genuine response in the person administering the fake torture?