Blackmail

Much of the filming originally was shot silently. When sound became available during the course of shooting, Sir Alfred Hitchcock reshot certain scenes with sound, thus making it his first talkie. There was one complication with this change, however. Leading lady Anny Ondra had a thick Czech accent which was inappropriate for her character, Alice White. Joan Barry was chosen to provide a different voice for her, but post-production dubbing technology did not exist then. The solution was for Barry to stand just out of shot and read Alice's lines into a microphone as Ondra mouthed them in front of the camera. [This is a major plot point of Cantando bajo la lluvia (1952), which is set in the era of movie studios moving from silent pictures to talkies.] This generally is acknowledged as the first instance of one actress' voice being dubbed by another, even though the word "dub" is technologically inappropriate in this case.

When Alice "unlocks" the door to the building where she lives, it starts to open as soon as the key reaches the door. It was clearly not only not locked, but not even latched. However, she goes through with the motion of unlocking it.

Originally filmed as a silent movie, running 75 minutes; Hitchcock later added newly shot scenes and had other existing footage dubbed to create a talkie version, running 86 minutes.

Edited into Der Zinker (1931)