Revealing mistake: The birds that attack the schoolchildren have no shadows. (01:13:40)
Revealing mistake: Towards the end of the film, when Hilts (Steve McQueen) is in a motorcycle chase with the German guards, if you watch closely, when the camera cuts away from Hilts and to the German motorcyclists, you might be able to notice that one of the guards chasing McQueen IS actually McQueen! They used him to play one (or maybe more) of the guards because of the experience he had with motorcycles. This can also be seen in some behind the scenes footage on the DVD version of the film.
Revealing mistake: During the fight on the train between Bond and Grant, you can spot the stunt double for the Grant character by noticing the bad toupee.