Revealing mistake: When Chang's paint bomb explodes, pay attention to the background. You will see paint exploding from three different points on the ground. (One to the center, one to the left and one to the right) The only problem is that there was only one paint bomb in the center, so it makes no sense that there are 3 explosions from different points.
Continuity mistake: At the end when Abed is talking to the Dean, there's an open to-go box with chicken fingers. After the Dean asks who would steal a box of hairnets, it cuts back to Abed and the box and ketchup are gone. Post-it notes are also now seen and the stapler moved. In the next shot of Abed, the chicken is back.
Continuity mistake: When Jeff and Abed are talking in his room, the amount of the root beer float in Abed's glass changes. Especially noticeable is when Jeff leaves, the float goes from near the top and above his fingers to a couple fingers below.
Continuity mistake: After the pottery class scene, in the Spanish classroom, when Britta and Jeff are talking, his right arm is across the desk. When Jeff replies "so did someone's psych teacher" and camera cuts, his arm is suddenly folded up by his chest. In the next shot, his left hand is suddenly over his right hand.
Continuity mistake: When Jeff and Pierce are having a glass of whiskey, Pierce makes a toast and Jeff replies "To the irony of that sentence." After he says this, Jeff puts his glass back on the table and Pierce lowers his glass, but doesn't put it back on the table. In the next shot, Pierce's glass is suddenly on the table.
Visible crew/equipment: After Britta accidentally bumps the gurney into the window, she grabs the body bag in a failed attempt to keep the corpse from falling out into the quad. Right as she grabs the body bag, look on the ground behind her. Someone slides a mat in behind her for her to fall onto.