When writing her name on the sign up sheet for the glee club, Tina adds extra Ts at the beginning to mimic the stutter that she often speaks with. When Rachel comes to write her name underneath Tina's the extra Ts are gone and Tina is written properly.
The two men in the photographs in Rachel's locker of her with her dads don't even resemble the actors who later played them.
Sandy Ryerson says he got medical marijuana to treat his nervous breakdown. Ohio does not have medical marijuana yet. Michigan does, but bringing it across state lines would be a felony.
After Finn claimed his mother was having his prostate removed while actually going to Glee, Puck confronts him and claims "Chicks don't have prostates, I looked it up." However in a 2002 medical research study, it was found they do.
When we hear the narration by Rachel in the beginning of the episode, she states that she tries to post on MySpace everyday to keep her talent alive and growing. However, when the Cheerios are watching Rachel's cover of "On My Own", in the box that says "Similar Videos", it states that there are no other videos from Rachel.
Vocal Adrenaline is announced only as last year's regional champions. They were the reigning national champions at that point (revealed later).
During "Don't Stop Believing," as Finn finishes playing the drums, he stands up and hands the drumsticks to the drummer, but we hear the drum fill continue while there is clearly no-one playing.
When other students sign their names to the Glee Club sign-up sheet, we see Artie's name has been written as "Arty".