Revealing mistake: When the mayor has his head shaved by the Grinch, Clint Howard grabs the clippers and shaves his own head down the middle. His hair is yanked off his head before he even moves his hand. Even better in slow motion.
Revealing mistake: When the Penguin is sliding down the zip line, just before he hits Batman you can see Batman throwing a punch at nobody, he is swinging at empty air.
Revealing mistake: Lizzie has black nail polish and the same size of nails throughout the entire movie. Supposedly, Lizzie and Isabella are different people. But, when Isabella comes back, you can see she has the same color nail polish and the same size of nails as Lizzie. I don't think it's just a coincidence.
Revealing mistake: At the beginning when the ruler is making his speech, you can see his modern day fillings in his upper molars.
Revealing mistake: When the Pterodactyl is flying around with the egg, its shadow isn't cast as she flies over the trees.
Revealing mistake: When the elephants are making fun of Dumbo in the train caboose, Dumbo's mother pulls a pin which causes the stall door above the other elephants to fall. When the door bounces back up, you can see that the animators forgot to draw the elephants' heads and trunks and only their bodies are visible.
Revealing mistake: When Rufio brings the sword down on the rope holding the slingshot, you can hear the intended sound effect, but the rope is not cut. (01:05:20)
Revealing mistake: In the scene where Rudolph is saving Tony from the truck he says, "close your eyes, Tony". But in the next scene when they are on the blimp the boys introduce themselves. Rudolph did not yet know Tony's name but yet he said it.
Revealing mistake: When one of the men picks up Garfield from his cage to display to potential buyers at the pound, you can see the man's right hand "entangled" with the computer-generated Garfield.
Revealing mistake: At the bank there is a close-up of Mr. Darling with Sir Edward Quiller Couch standing behind him to his right, just as Nana, et al. are about to collide with the bankers. The camera pans in for the extreme close-up of Mr. Darling, who makes a horrified face. Later, when the Darlings are at the party Nana bursts in. Sir Edward again stands to Mr. Darling's right. Mr. Darling puts his hands up in front of himself and the next close-up shot is the very same shot from the bank. Part of Sir Edward's hair is edited and the background is digitally augmented. (00:09:25 - 00:23:20)
Revealing mistake: When Tom joins Sarah and Eliot for the kneeboarding, after Sarah apologizes for Tom's interrogation Eliot says, "It's okay, my dad would've done the same thing." Two shots later, as Tom grunts in the water, this shot is flipped - the driver is now on the left and the kids switched sides.
Revealing mistake: When Mia is playing softball in gym class, and the ball she hits at Josh hits him in the groin, he actually gets hit in the stomach. (01:24:45)
Revealing mistake: When Violet and Klaus make the tent inside their bedroom in Count Olaf's house, they set up the light with the faces of their parents on it in front of it. Except when it shows the shadow of the object outside the tent, the edge of the picture frame isn't showing when it should. (00:21:40)
Revealing mistake: When Number 5 is leading Number 3 into the toilet and moves at the last minute, you see Number 5 falling over, but in the next scene, he's perfectly fine.
Revealing mistake: After Mitchie wakes up at the start, her hand slides across the keyboard keys in the close-up, but that hand is not Demi Lovato's. The older looking hand has protruding veins and the fingernails are long, whereas Mitchie's nails are short and her hands look as young as she does.
Revealing mistake: In the hotel meeting scene, the Grand High Witch tells the witches they can take their wigs off. When we see the newly bald witches, it is particularly obvious that only the foreground witches are ladies with bald caps - the rest of the witches are bald men. (00:30:10 - 00:31:00)
Revealing mistake: When all four actors are up on the rooftops, look closely at them when they all step onto the smoke platform that brings them down. All four actors are doubles. (01:46:50)
Revealing mistake: At the end, when the train destroys the time machine, right at the moment when it hits you can see a small explosion, which was used to trigger the destruction of the time machine. (01:43:03)
Revealing mistake: While Miss Hannigan is singing "Little Girls", she sees one of her foster girls as a lamp on a table. As the camera and scene continue down the hall, a foot can be seen in the background as the girl jumps off the table to be replaced with a real lamp.
Revealing mistake: When Scooby, Shaggy, Mary Jane, and Daphne go crashing through the window while running from the two monsters, the falling glass and broken window frame pass right through the CGI Scooby. (00:42:30)