Continuity mistake: Boo shows a drawing of Randall. First, it's held in a portrait position, then in the reverse angle, it is now held in a landscape position. Then back to portrait position in the next shot. (00:31:30)
Continuity mistake: Waternoose grabs a scream can and starts releasing all the energy and the red line starts to go down. There are white lines over sections of the can. When he begins to release the energy, right at the very end of the first shot, the red line that goes down has not yet reached the first white line. In the very next shot, the red line has suddenly passed the white line.
Continuity mistake: After Mike sprays his eye with the disinfectant it goes red, but just after he snatches the doll from Boo, his eye is fine again, and then goes back to being red for the rest of the scene.
Continuity mistake: When Sully and Mike are talking in front of the Abominable Snowman, and Mike starts throwing the snow cones at Sully, we see the snowman covering one of the snowcone holes with his thumb, while from a different angle it seems as though his thumb is between the two holes and the hole that he had just covered has an empty snowcone wrapper in it. (01:00:35)
Continuity mistake: The scare chart shows a picture of the scarer and the number totals. In the shot that shows Mike repeatedly taking out tanks whilst Sulley is scaring the child, the names of the people have suddenly appeared next to the pictures of the scarers that weren't even there in previous or following shots. This only happens in the international version.
Continuity mistake: When a green monster named Frank was walking out of Monsters, Inc. on the second day, take a look at what's behind the door - It only shows passages to scare floors, but when Mike and Sulley (holding Boo in costume) walk in, the CDA is all over the place. (00:35:05)
Continuity mistake: Near the end of the movie when Waternoose "calls" for Boo's door along with the CDA, it arrives into the factory on the "outgoing" door track.
Continuity mistake: There is a purple chair and a green chair in Mike and Sulley's apartment. The green chair disappears when they are at the apartment with Boo later. (00:05:45 - 00:27:50)
Suggested correction: Didn't they use the chairs fabric to make Boo's disguise? The chair would have been ruined.
They only used Sulley's chair to make a costume for Boo. Mike has his own chair but we are never shown as to where he keeps the chair. He may have put the chair somewhere else in the apartment so Boo wouldn't her germs all over it.
Continuity mistake: When George comes out of the door with the kid's sock stuck to him the sock's toe points inward toward the middle of his back. When the CDA rushes in to remove it the sock toe faces outward. (00:17:40 - 00:18:25)
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.
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.
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.
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.
