Continuity mistake: In the scene where they are in the all you can eat restaurant, when PaPa Klump farts into the candle causing the curtain to catch fire, when they first show the curtain after the 2 men put out the fire, there is clearly a burn mark on the edge of the curtain. However, when they show the curtain again, there is no burn mark. (00:17:25)
Revealing mistake: In the scene where the Klumps go to the "All you can eat" restaurant, Sherman sits at the corner of the table next to his father. When he sits he puts his hands on the table. His father does the same, but because the actor is edited into the scene the fathers hand goes through Sherman's hand. Both hands are on the same place on the table, and you can see through them. (00:12:10)
Visible crew/equipment: After the disastrous experiment with the giant hamster, Miss Guilford approaches him, and the cameraman can be seen walking behind her in the reflection on the side of Buddy's car. (01:17:05)
Continuity mistake: When they are at the all you can eat restaurant, and grandma is using a piece of spaghetti as a joke against Cletus, in the long shots looking at grandma, the noodle is about 3 inches long, however in the shots from directly behind grandma, it is about 6 or 7 inches. (00:16:10)
Continuity mistake: At the end of the movie when Denise is looking for Sherman at his house and she's asking Papa Klump where he is, Papa Klump says he was talking about eating some guy and then she figures that's Buddy. But when she figures that out she grabs the newspaper Papa Klump is wiping his hands with and opens it and sees Buddy's picture on it. Now how did she know Buddy was on the newspaper when Papa Klump was wiping his hands with it before he told her that? (01:27:20)
Factual error: In the scene with the giant hamster, the hamster is making squeaking noises. These unique noises are actually made only by guinea-pigs, not hamsters. Hamsters don't make any sounds at all. (01:14:45)
Factual error: In the scene where Professor Klump comes into Denise's classroom while class is in session, he is making his way through a bunch of students trying to get to a vacant seat. On stage, the shadow of Klump goes across the viewing screen as if he is walking through the projection of the overhead projector. The problem is, the overhead projector can be seen on stage with Denise, so how could Klump have walked through the image?
Continuity mistake: When Sherman plucks Buster's hair out of the ooze, it is grasped at the very end of the tweezers, yet in the next shot it is held further down. (00:39:40)