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: Though the loose ferris wheel keeps rolling for over a mile, the guys seated on it remain in the same position all the time instead of rolling down and getting crushed by it. Furthermore, they disappear in the wide shots and the wheel appears empty.
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.