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.

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: When Mike and Sully are in the ice cave, and Mike is starting to throw the a Snowball before Sully says, "None of it matters anymore" the snowball turns from yellow to white for a few seconds, and then back to yellow.

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.

Continuity: At the start of the workday, Randall opens the first door with the knob on the left and hinges on the right. When he comes back out, the knob is on the right and the hinges are on the left.

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 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.

Continuity: When Randall catches Mike and tells him that he has half an hour to put Boo in her door he also says the door will be in his station. Later we see that the door is on station 5. But on the first day Mike and Sully are working on station 5 and Randall is on station 6.

Factual error: After Mike rebuilds Boo's door, it shows a few crack lines but is otherwise intact. But the shredder created a lot of sawdust so it would be impossible to rebuild the door using only the wood pieces.

Factual error: The map of the world on the scare floor shows Australia without Tasmania. This is best seen late in the movie after Boo has returned home, Sully is now management and when Mike asks him to follow him you can clearly see the world map behind Sully showing Australia and no Tasmania.

Continuity: 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.