Character mistake: Poirot identifies Prof. Hardman's revolver as a 1927 police-issue weapon due to its blued finish and chequered grips. In fact, these features were common in the widely-available civilian versions of the Colt 'Police Positive' revolver and not the least bit specific to police-issue weapons.
Character mistake: At the beginning of the film, the officer states that the kid taken was named Jeremy Jenner, when he was in fact named Darius Jenner.