Revealing mistake: When Matilda telepathically makes the TV explode, you can see what looks like parts of an explosive hidden behind the screen.
Suggested correction: Clearly no sign of it.
Suggested correction: There is no view of the explosive.
Suggested correction: When the TV set explodes, it's a close-up of the screen and no device is seen. When it changes to a wider shot of the actual explosion, the glass breaks and some components of the TV set are shown. There is no way to distinguish between what is a component and what is, as you say, an explosive.
Revealing mistake: As the Wormwoods are driving out of the hospital parking lot at the beginning of the movie, the shot of the car driving from right to left has been flipped, as evident by the quick appearance of a hospital directory sign in the background being mirrored.
Revealing mistake: When Matilda goes to the Trunchbull's house alone to get the Lissy doll, she's sitting on top of what looks like a garage, Matilda leans forward and presses down on the roofing shingles but they bend in a way that shows they are foam, not real shingles.
