 A shill in a psychology experiment, or the like, is called a "confederate".In Stanley Milgram's experiment, in which the subjects witnessed people getting electric shocks, a confederate would pretend to be one of the experimental subjects who would receive the fake shocks, so that the real experimental subject would think that a draw of names from a hat was random.The confederate would always play the role of the learner, and the subject would be the teacher, and the subject would think that this was a random draw from a hat containing papers that say "learner" and "teacher".