Continuity mistake: Near the beginning Harriet Vane produces tokens for herself & Lord Peter Wimsey of miniature handcuffs with one cuff "open to symbolise we're giving up on crime". She puts hers on as a bracelet. Immediately after & several times throughout the film it's clear hers is a set of closed handcuffs.
Continuity mistake: In the beginning, in the hotel foyer, at Monte Carlo, the girl has a cup and saucer in her lap. When Maxim joins them, the girl is holding the cup and its handle is on the right, then she's not holding the cup, it's just resting in her lap, then she's holding it and the handle is on the left.
Continuity mistake: The car the deputy and contractor drove up in disappears. That road was one lane which would have been a hell of a back up job. Then almost instantly the 2nd car full of deputies flies up like a bat out of hell "hey what's going on" indicating they didn't speak to the contractor because they had no idea what occurred. The next sequence Casey points in direction from where the deputies just flew up. The complete opposite of where the woman was actually lying. The poor woman would have been ran over. (01:11:53)