Revealing mistake: Our heroes arrive at an RAF base. Purdey hears a loud aircraft noise and looks up to the sky - cut to shot of a fighter jet. For a few frames after the cut, a caption that reads "The Engineer in the RAF" is just visible. It would seem they 'borrowed' some material from an RAF training film. (Indeed, a later shot of shells exploding was obviously taken from a videotaped TV programme, judging by the 'lag' effect caused by the tube camera that would've been used).
Revealing mistake: In the arcade the killer talks to his helper while playing a pinball machine. He plays very agitated and strongly. But if you look closer at the below end of the playfield you see that there is no ball and the flippers aren't moving. (00:23:50 - 00:24:48)