Danny Pudi and Donald Glover recorded all of each others' dialogue so that the other could listen to it prior to filming to get the tone and mannerisms exact.
Britta's pajama top is the same t-shirt she wore while with Annie during the oil spill fundraiser in The Psychology of Letting Go (2010).
In the opener, Abed is wearing a "This is Not My Time Machine" tee. At the top, Bill and Ted from Bill & Ted's Excellent Adventure (1989), are with the Tenth Doctor's Tardis, and below them, the Tenth Doctor is with their phone booth.
In the opener, the whiteboard behind Annie and Shirley is signed "Welcome Back K. Otter" an obvious reference to Welcome Back, Kotter (1975).