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)
Visible crew/equipment: When the baby in the baby stroller is rolling down the cliff hills, a safety wire attached to it is briefly visible, as Luke chases after it.
Character mistake: When the Grand High Witch and her assistant enter her room while Luke gets the formula, they're wearing pointy shoes. Earlier, it was mentioned that witches never wear pointy shoes.
Continuity mistake: The position of the hood on the baby stroller as it rolls down the cliffside hills keeps changing from fully down, to halfway up, etc. as Luke chases it.
Audio problem: Bruno's mouth is out of sync when he says "I really do hate margarine," as he is talking to the waitress about what are in the sandwiches that day.
Continuity mistake: The position of the drawing Luke holds, as he lies down on the bed talking to his Grandma, changes. Also, the Grandma (Helga) picks one drawing up twice between shots.
Continuity mistake: A small brown card appears in the witch's hand, as she stands up on the stage and says that she smells dogs droppings, as the other witches are leaving.
Continuity mistake: After a witch is blown up in the RSPCC meeting, the size of the burnt hole in the chair changes for a shot, and so does the pile of black charred remains under the chair too.
Revealing mistake: Of the witches that are bald, the make-up's bald cap is much too obvious on some of them in many shots.
Continuity mistake: The way that Helga holds her bag as she waves it in front of the Jenkins' parents changes between shots, as she tells them she has Bruno inside it.
Visible crew/equipment: The scene where Luke is changing into a mouse, you can see the masking tape on the floor where Anjelica Huston's feet are supposed to be positioned.
Audio problem: When Mr. Stringer says "What the devil," as all of the sheets of paper on the reception desk start flying about, his mouth doesn't move.
Revealing mistake: The grandma, who has a missing pinkie, clearly has it in some shots, and in some scenes it is clear she is bending it behind to make it seem as though it is missing.
Continuity mistake: The amount (level) of chips in the bowl, which Luke (as a mouse) hides in keep changing, as the chef puts the bowl down on the trolley, to when the chef picks it up and carries it away.
Audio problem: Near the beginning, after Erica disappears and Helga visits Erica's mother, Erica's mother says "Come on in Helga, have some cake", but she is clearly saying something else.
Visible crew/equipment: When the witch throws the toy airplane back up to Luke, who is standing in the treehouse, a wire is visible attached to the airplane, guiding it up to him.
Plot hole: At the end of the movie, the witch's secretary returns Luke's pet mice to him even though she had no knowledge of their whereabouts or the fact that those two specific mice were his.
Suggested correction: Just before Luke and Helga leave the hotel, Helga gives Luke a tag with the address of where they live written on it. Luke took the tag and delivered it to the room where Miss Irvine was staying in. Miss Irvine is looking at the address as Luke and Helga leave the hotel. She most likely saw William and Mary at some point in the hotel and is clever enough to figure out that they're Luke's pets.
Audio problem: When Luke (as a mouse) finds Formula 86, we hear him say, "We got it, Grandma," but his mouth doesn't move.
Continuity mistake: At the end of the movie when the Grand High Witch's assistant watches Luke and his Grandma drive off from the window, she pulls the curtain and is not wearing gloves.
