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: 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: 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: 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.

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 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 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.

Continuity: After Boo falls asleep, when Sully says, "Hey Mike this might sound strange, but I don't think that kid's dangerous," Mike adjusts the lamp on the desk making the right bulb lower than the left. Next shot, as Mike turns, the right bulb is now higher than the left.

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: 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: During the scene on the scare floor, there is a world map above the entrance. To the right of the map are two signs that read STAND BY and SCARE. In some shots, the signs change from written words, to symbols of a monster standing still (STAND BY) and roaring (SCARE).

Continuity: In Sully's bed, Boo is afraid of the cabinet, and there are many drawings in the bed, but when she shows the drawing of Randal, the others are gone. They come back when she goes to sleep.

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

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: When Mike takes the toilet paper off his feet, it's lying on the floor in the hallway. But when his girlfriend comes and yells to him, it's gone.