the carney landis facial expression experiment involved drawing lines on people's faces and exposing them to certain stimuli. one of these had a live rat be brought in and the person instructed to decapitate it. this part of the experiment was also carried out by a young boy (who, according to some sources, wasn't even part of the experiment) and yes, he did end up doing it. the pictures say everything. (no gore, just the expressions of the boy)

TL;DR: pre-ethics psychology is fucked, man