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.
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)
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.
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.
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.
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.
Other mistake: When the evil witches get their just desserts, Lois Leffour's friend Julia Whitman is choking on the Formula 86 bottle. Even though the bottle is small, Julia should have either seen it on the spoon, or felt it when she put it in her mouth. Instead, Julia swallows the bottle and coughs it up during her transformation into a mouse.
Other mistake: Before the Grand High Witch starts the meeting, Luke is watching the witches sit down, and he doesn't recognize the Woman in Black. This doesn't make sense because the Woman in Black attempted to kill him during the treehouse scene before any of them arrived at the hotel. The Woman in Black is even the first witch who tries to capture him when he runs on the stage.
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.
