You've probably heard of the Stanley Milgram shock experiment, in which 26 of 40 (65%) of subjects willingly administered shocks of 450 volts to a test subject when prodded by the experimenter.
Of course, the shocks weren't real, and the people purportedly being shocked were in fact actors, but the subjects didn't know that. Yet, not one of them refused outright before 300 volts -- by which point the test subject (heard, not seen) was already clearly in agony (the starting voltage was 45v). In addition, none of the 40 subjects insisted that the experiment itself be cancelled, or went to check on the health of the shockees.
After the publication of the experiment, some commented that the subjects must have known the actors were faking, so... a follow-up was conducted (King & Sheridan, 1972) in which shocks actually were given to real subjects: puppies. (In addition, the study has been replicated many times since, consistently yielding ~65% willingness rates).
Now, clearly nobody believes the puppy is faking it. As I understand it, the puppies were actually present in the room, unlike the human subjects previously. So, how many of the 13 male and 13 female college students delivered the maximum, potentially-lethal shocks? Guess before you read on.
According to Wikipedia, although many of the women were highly emotionally distraught (and some cried), all of the females pressed on until the end, as did 7 of the 13 men.