Continuity mistake: In the scene where Mike and Sully are in the locker room after a day of scaring, discussing plans for the evening, George Sanderson's assistant is seen in the lower left side of the screen, having difficulties removing his helmet. In the scene immediately after, Mike and Sully are walking down a large hallway that leads to the Monsters Inc. main lobby. George's assistant is seen in the background in the hallway, wearing his helmet. Even in the shot where Roz is inquiring about Mike's paperwork in the lobby, the assistant is still seen crossing the lobby in the background, wearing his helmet.
Other mistake: In the door vault scene, Boo's laughter causes all the red lights on the doors to generate and fully power. Unlike the other two scenes - back at the apartment and the trash compactor - this resulted in a blackout. (01:09:09)
Suggested correction: In the house and at the compactor, it caused an overload. This resulted in a blackout. The doors seem to work differently.
Other mistake: The scare leaderboard shows scarers by their surnames, except Randall, who is shown by his first name only.
Continuity mistake: When we first see Waternoose, he says a single touch of a child could kill them. A yellow guy throws his pencil and pad forwards out of his hands. When Waternoose walks over to the three people, the pencil and pad has moved to the right of the yellow guy without ever being touched.
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.
Continuity mistake: When Mike is performing his standup routine in a boy's room near the end of the film, his eye quickly switches from green to blue, and then back to green right before he says "your room."
Continuity mistake: When Sully and Mike are practising, their chairs are switched. Sully's is on the right Mike's is the left. When they sit to watch the commercial, they are switched back.
Character mistake: When Mike pulls out the first Scare Report, the word "yield" is spelled wrong.
Continuity mistake: When they go to the Scare Floor to put Boo back in her door, Mike swipes the card key and the numbers "240492" appear on screen. In the next shot, the numbers on screen are now "43496". (00:39:10)
Continuity mistake: In the apartment, Sulley leaves a trail of Kreature Krisp for Boo to follow. The first one he places is white, which becomes green in the next shot. It's obviously the same one in both shots because of its position in the doorway. (00:31:00)
Continuity mistake: Two people put an employee of the month picture of Mike and Sulley on the wall. The photo is noticeably crooked. In the shots of the two people talking to Mike and Sulley, the photo is correctly positioned without being touched.
