One's first inclination might be to argue that there must be some sort of built-in animal aggression instinct that was activated by the experiment, and that Milgram's teacher-subjects were just following a genetic need to discharge this pent-up primal urge onto the pupil by administering the electrical shock.
adj. 被压抑的； 被抑制的
He still had a lot of pent-up anger to release.
the sudden outpouring of pent-up emotion
She was too pent-up to speak.
I've been pent-up in this office for over a year.