In his autobiography, Christopher Lee claimed that Robert Siodmak changed the original screenplay: "The script started life as serious, nay solemn, but Robert Siodmak, the director, with all the sure touch of real tension behind him in The Killers and The Spiral Staircase, took stock of the material in forty-eight hours and turned it into a comedy."
Ojo (Nick Cravat) is mute because Cravat had a thick East Coast accent.