Revealing mistake: Just before Anthony Dawson is going to be stabbed to death by Grace Kelly with a pair of scissors, you can see for a very short moment that the scissors are already attached to his back.
Dial M for Murder (1954)
1 revealing mistake
Directed by: Alfred Hitchcock
Starring: Ray Milland, Grace Kelly, Robert Cummings, John Williams
Continuity mistake: When Tony throws the 100 pounds down-payment across the room to Swan, watch the chair in which it lands. It has a low back one in one shot, then a high back (probably to provide a bigger target for the throw), then a low back again.
Mark Halliday: What is all this?
Chief Insp. Hubbard: They talk about flat-footed policemen. May the saints protect us from the gifted amateur.
Trivia: Alfred Hitchcock wanted the film to look as natural as possible, with the camera at eye level with the actors. Since movie cameras were large (especially 3D cameras), Hitch had a small trench built into the soundstage floor, so that the camera lens was, roughly, at eye level.