"Modern Warfare" was so beloved that the show pushed even harder into the parody realm in season 2, including a three-week stretch featuring both "Basic Rocket Science" (the study group gets trapped in an "Apollo 13"-style situation on a flight simulator) and "Epidemiology" (tainted meat turns most of the student body into zombies). But some of the best high-concept episodes of that season, and the run, focused less on the concept than the characters. To compensate for the expense of a space mission gone awry and a zombie attack, the show did a classic bottle episode, taking place entirely inside the study room and featuring only the regular characters. But even as Abed kept noting that they were all in a bottle show, the story — in which Annie forces the others to stick around until someone confesses to stealing her pen — turns into a hilarious, moving excuse for all the members of the study group to confront their issues with one another, until everyone is stripped down both literally and emotionally.