Deliberate "mistake": When Boo laughs repeatedly while playing hide-n-seek with Sully in the men's room, nothing happens to the electricity - no surges as with all other times she laughs. [In the audio commentary by the directors, they explained that it would've been distracting if an energy surge occurred every time Boo laughed, so they simply didn't address the issue. A reasonable course of action, but still a mistake.]

Continuity: After the Scare Floor shuts down at 6:00 and Sulley goes back to do Mike's paperwork, the clock reads 5:48. After he returns again to put Boo back, it clearly shows 5:48. Finally, after Randall leaves and Sulley leaves the Scare Floor for the restaurant, the clock reads 6:48.

Continuity: In the opening scene, on the floor there is a toy train on circular tracks when the monster sneaks in. When the monster trips backwards over the ball and skateboard then falls onto the jacks, the train and tracks are gone.

Continuity: When Mike is bringing Sully to the fixed door he has no slivers or band-aids on his hands, then when he says "it was a lot of wood to go through" you see he does.

Other: Near the end of the film, when the identity of 0001 of the CDA is revealed, number 0112 is shown both standing next to 0001 as she enters the room and behind Sully and Mike on the opposite side of the room.

Other: In the scene when Mike, Sully, and Boo were all hiding from Randall in the bathroom, all three of them are standing on the toilet in the same stall. They look straight ahead and see Randall using the sink in front of a mirror. But, a minute later Randall is busting open the door to each stall. When he hits their stall door open, he is looking the other way, and doesn't see them. Yet he would have seen their reflection in the mirror. I realize that Randall's eyes were not looking straight ahead into the mirror. But, where he was looking, he would have easily seen a huge, bright blue and green monster.

Continuity: When Sully places the menu on the table he puts it face down (logo first), then when he lifts up the table, to quickly get Boo, the menu is face up.

Other: When Sulley and Mike take Boo into the Factory, they see all of the CDA agents. There are 3 talking to Mr. Waternoose(as we see seconds later). One of them is number 00002. When they are done, they escort Mr. Waternoose to somewhere else. However at that very second another agent comes in with a metal detector thing. His number is 00002.

Continuity: At the beginning of the film, we see Sully asleep in his bed and the alarm clock/radio on a bedside cabinet to the right. Later, when Boo climbs into Sully's bed, the clock/radio isn't there anymore.

Continuity: After Mike is throwing snowballs at Sully, there are 4 empty cones, then there are 3, and then 4 again.

Other: In the scene where Mike and Sully walk in on the CDA overrunning the power company, there is a CDA agent with number 00112 behind the main desk, and another with the same number talking to the boss a second later.

Continuity: At the beginning when the monsters are at the testing room, you can see the boy in the bed seeing something opening the cabinet. He closes his eyes and opens them up again to see a sweater sticking out. But when another monster sees what he does wrong on the tape, the sweater isn't sticking out anymore.

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.

Continuity: During the ending credits, they show Mike and Sulley redoing their "musical" number in front of all the monsters on the scream floor. During this Sulley blocks Boo out of the way by pushing her behind him. But when Sulley starts to dance, Boo has disappeared.

Continuity: At the beginning when you see the monster in the testing room from under the bed with the glowing eyes, you also see the soccer ball on the left side of the screen. This shot takes place on the side of the bed. After the monster gets scared, he backs up kicks the soccer ball, but it is now at the foot of the bed in the middle of the room.

Continuity: At the start, when the simulation is terminated, as Phlegm pulls a jack off his back, the large checkered rug at the foot of the bed is gone. It should be seen on the floor in front of him, in this shot facing the wall as it goes up.

Continuity: The monster that operates the doors for Randall, has legs that bend back like a bird's, but in the shot when Sulley saves Mike from the scream-extractor and puts that monster where Mike was, he is sitting down and his legs bend forward.

Continuity: When Boo is in Mike and Sully's house, it's a "jazz" poster on the wall near the door, but when Boo is crying, it's gone.

Continuity: When Mike and Sully first come to the work, you can see two big monsters who talk near the reception, but Cilia is not there. But when they come closer, she is there.

Factual error: In the scene where Waternoose and Sully are talking, Waternoose gets himself some "coffee", which is sludgy and thick and takes quite a while to pour from the machine. Seconds later, he takes a very quick sip. Since the liquid was so thick and there was little in the cup, it would be impossible for it to pour that fast.