Audio problem: When we see Mike during the slumber party, we hear seven bells ring for the seven filled cylinders, but there are only six cylinder-filling noises. (00:16:50)
Audio problem: When Mike and Sulley walk through Monstropolis, Mike goes to his car. An automatic unlocking sound from the car, but the keys Mike is shown holding appear to be the keys one would use to manually unlock the door. (00:07:20)
Suggested correction: Monstropolis is shown to have many things that operate differently from the real world. It isn't such a stretch to consider that car keys work differently as well.
Audio problem: Jerry counts down from seven. When he has to say one his mouth opens, but he doesn't actually say one. (00:14:38)
Suggested correction: Many times when counting down, three-two-one is silent.
Especially when filming something like this, so the numbers aren't accidentally recorded.
