In one scene Grandpa packs up all of Arnold's stuff, but in the scene when Arnold and Gerald have a sleepover all of Arnold's stuff is suddenly back in his room.
There's a scene where Arnold is talking about saving the neighborhood, while Helga is on the roof of a building talking to herself. Arnold is in the street, and there's a man in a white tank top standing in front of him. In another shot, the man is standing behind Arnold, and Helga shoots a plunger at his head. Then in the next shot, the man is back in front of Arnold and his head doesn't have the plunger on it any more.
When Big Bob throws a model of Arnold's house in the trash it lying on its back but when it shows it again it is standing up straight.
When Big Bob first asks to keep the pop-up version of the Arnold's neighborhood, he picks up Arnold's house and on the roof it only shows the sky window. Once it gets thrown in the trash the shed suddenly appears next to the sky window.
When Gerald is lowering Arnold down into Nick's apartment to get the key off him his wrist watch starts beeping showing it's 1am in the morning. Afterwards, when they talk with Deep Voice on the phone he/she says it's 2am.
In the video surveillance room, Arnold presses the record button to eject the tape of Sheck burning the tomato document.