In the finale song "You May Be Right", an extra in hospital scrubs is seen trying to slip past Blaine on his left as Blaine dances next to Mr. Schuester. After a quick cut to a panoramic view of the school hallway, no one is next to Blaine at all.
The position of Jake's arms changes with each camera cut as he sits watching Marley during Ryder's performance of "Innocent Man".
Unique claims to have never heard of Billy Joel, then less than a minute later in the same scene, she dances in perfect time and sings backing vocals to the Billy Joel song sung by Blaine and Sam.