Revealing mistake: At the end of the film, the screw is tapping on the window to get out and Hogarth moves to put the box down. The box completely vanishes from the shot for a few frames towards the end of the shot.
The Iron Giant (1999)
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Directed by: Brad Bird
Starring: Jennifer Aniston, Vin Diesel, Harry Connick Jr., James Gammon
Continuity mistake: When the Iron Giant follows Hogarth home they cross a railwayline and the Giant starts to eat the steel rail. During this scene you can see the distance of the railway sleepers changing from a fair distance apart to close together over the course of the shots. In the same scene you can also see that, although there is a crossing with lights, no vehicle could possibly pass as the rail has no crossover facility at that level. (00:24:30)
Dean McCoppin: Oh, hey, I know you. Squirrel boy.
Hogarth Hughes: Uh, Hogarth.
Dean McCoppin: By night known as Hogarth.
Trivia: After Mansley's car is eaten by the Giant and disappears, Mansley is trying to get Marv to look at it but doesn't realise it's gone yet. Marv then asks, "What are we looking at here, Manly?" leaving out the S in Mansley to call him Manly. This was a mistake on the voice actor's part, but Brad Bird liked it and thought it appropriate for the character, so left that take in.
Answer: Turn back to/from what? Can you please expand on the question so we know what you're referring to?