"Epidemiology" is the sixth episode of the second season of the American comedy television series Community, and the 31st episode of the series overall. It originally premiered in the United States on NBC on October 28, 2010 as a special Halloween-themed episode. In the episode, the Dean throws a Halloween themed party on campus. During the party, a few of the partygoers become sick from eating a hazardous substance that the Dean mistook for taco meat bought at an army surplus store. The sickness causes those affected to turn into a violent, zombie-like state that can be passed on through bites. As the study group try to escape, the Dean (under orders from U.S. Army Special Operations) locks the doors, trapping them inside with the infected.