Revealing mistake: In the scene where Sgt Howie hits McGregor (who is dressed as Punch) with a candlestick, watch closely and you can see that the blow from Howie is aimed into the padded section on the back of the punch costume, rather than at the back of McGregor's head.
Revealing mistake: The sliding door to the bedroom in Simonson's apartment appears to be covered with a sheet of 'bubble wrap' in early scenes of the room.
Revealing mistake: Right at the end when John is dying look at the texture of his blood. It is way too thin, almost like coloured water.
Revealing mistake: When Jack Hawkins punches through the door it is very apparent that it's made of very thin wood to make it much easier to hit through.