During the anthropology class, the content on the blackboard at the front of the class is different before and after Professor Ian Duncan enters the room.
In the credits when Jeff comes in, Troy and Abed look next to the camera holding their cups up, then in the next camera they do the exact same thing again, but this time it's focused on them.
Troy's arms suddenly fold themselves between shots when he is talking to Andre.
Jeff mentions that he knows Rich for almost two years. But Jeff meets Rich at near the end of season 1 in pottery class. This means that Jeff knows Rich for almost one year, not two.