Deliberate mistake: When George spies on his hedonistic neighbor down the hill with his telescope, the telescope is always level when it actually should have been pointing downward. Same when his neighbor spied on him - his telescope was always level also when it should have pointing upward.
Deliberate mistake: When Betty falls in the traphole, Maxine is right behind her, yet when the angle changes she's not only in front, but has turned 180ยบ. This allows for a funnier gag, but is still a mistake.
Deliberate mistake: In the basketball scene against Camp Mowhawk, the Mowhawk players' shorts have been pulled down a little, making it easier for the Camp Northstar players to pull them down all the way.