Audio problem: Troy asks if he can be a surprise witness, and then says "Wait." We hear him say this, but don't see him open his mouth to say it. (00:19:10)
Basic Intergluteal Numismatics - S5-E3
Revealing mistake: When Annie and Jeff think to search people who like Dave Matthews Band, she gets on the computer and starts typing. But the characters that show on the screen and the way that she types do not sync up correctly. (00:08:50)
Analysis of Cork-Based Networking - S5-E6
Continuity mistake: As Professor Hickey is waiting on the janitor to finish his meal, he looks away towards the hallway. After the janitor speaks, the camera cuts and he is now looking directly at him. (00:03:05)
Analysis of Cork-Based Networking - S5-E6
Continuity mistake: Abed opens his locker to reveal Britta's spoiler sheet. It rolls open but it doesn't fold open to see what it says exactly, but two shots later it is now open fully. (00:05:30)
App Development and Condiments - S5-E8
Continuity mistake: There is a gavel with its handle facing inwards toward the table, facing away from Jeff. When the app developers begin their pitch, the handle of the gavel is now facing towards Jeff. (00:01:00)
App Development and Condiments - S5-E8
Continuity mistake: Professor Hickey is rolling up a newspaper in front of him, when the camera cuts away and then back, it is flat against the table. (00:02:00)
App Development and Condiments - S5-E8
Continuity mistake: Jeff is doing stand-up comedy with a mic stand an a stool with a bottle of water on it behind him. A few shots later, without touching them or anyone moving them, they all completely vanish. (00:12:55)
Continuity mistake: Chang's sunglasses are sitting on the table in front of Professor Hickey and Shirley. When Richie sits down, the sunglasses have disappeared. (00:10:10)
Answer: His attempt to "kill" Jeff was to roll at him as an iPad on a stick. He knew it wouldn't work, but it played to the story that he was a killer as he knew Jeff would tell people about it, or attempt to retaliate for it.