 Siodmark later argued the only element he kept from the play was of a character disguising himself as an ape; the notion of fluid taken from the spine to cure a crippled girl was all Siodmak's.Filming began August 6, 1940, the final feature in Boris Karloff's six-picture contract with Monogram, returning only once for "Frankenstein 1970" (1958).Filming took a week.