Continuity mistake: There is a scene where Hugo is on the station and sees a key down on the tracks. There are two separate shots of the key and both times it is buried in the stones next to a sleeper. Then Hugo jumps down onto the tracks to pick it up and its now sat on the middle of the sleeper when he picks it up. (01:22:30 - 01:23:10)
Continuity mistake: When Hugo's uncle comes in to deliver the bad news he takes the pocket watch and puts it in his pocket. He then takes it again after he stumbles into the clock.
Continuity mistake: In the Library scene where the two kids are examining the old film buffs book, the book is first opened to a page with a bookmark, but the next scene the bookmark is gone.