Kurt is nowhere to be seen, and there is an empty chair between Blaine and Mike Chang until Holly's song starts. Then he is sitting in what was the empty chair next to Blaine.
The US devices that Puck wears on his collar are for officers, not enlisted airmen. Enlisted US devices have a circle around them.
The light blue shirt Puck is wearing during the Keep Holding On song would have the same rank insignia stripes as the dark blue uniform jacket he is seen wearing earlier.
During the Defying Gravity song neither Rachel, Mercedes nor Kurt hit the high note mentioned by Rachel earlier.
When Santana talks to Britney about how she is not being herself during the chess match, Britney moves twice in a row without letting her phone take a turn.
Sam tells April he is left-handed before the vote, but he is seen elsewhere throughout the show writing with his right hand.