- Anny Ondra's voice was dubbed by Joan Barry because Ondra had a thick German accent. Barry had to stand just off the set and read the lines into a microphone as the film was shot.
- In one key shot, the villain Cyril Ritchard is photographed with a thick shadow (caused by the arm of an overhead chandeleir) across his upper lip. Hitchcock wanted the image to evoke the old-fashioned, heavily mustached villain found in many silent films. He later called this touch "my farewell to silent pictures."
- Much of the film was originally shot silent; when sound became available during the course of shooting, director 'Hitchcock, Alfred' re-shot certain scenes with sound.
- being bothered by a small boy on the subway.
- Generally acknowledged as the first British talkie.
- The light levels in the British Museum were insufficient to allow Hitchcock to film the final chase scene in the museum. Without informing the producer, Hitchcock used the Schufftan process (developed by German cinematographer Eugen Schufftan). This involved taking still photos of the interior of the museum, then reflecting the photos in a mirror with certain parts of the silvering of the mirror scraped away to allow people (entering a door, for example) to be filmed through the mirror so that they appeared to be present in the museum. (In later years, American development of traveling matte and other process photography methods largely replaced the Shufftan process.)
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