The piece of piano music played by Francis Ingram (Victor Francen) and later, his disembodied left hand, is the "Bach Chaconne in D Minor", as arranged to be played by the left hand alone by Johannes Brahms. It was selected by Max Steiner because the story required a piece of music that could be performed by a pianist with only his left hand, and Steiner, who was born in Vienna and whose family were friendly with Brahms, rather than composing his own original piece, immediately recognized its potential in underscoring such a grim tale. Legendary Hungarian-American pianist Ervin Nyiregyhazi performed the music played by the severed hand.
According to Curt Siodmak in "Screenwriter: Words Become Pictures", he originally wrote the story for Warner Brothers leading man 'Paul Henried (I)' (qav). The actor decline,d saying, "I'm not wild to play against a dead hand." The writer believed that it would have been more effective with a good-looking man like Henried instead of 'Peter Lorre', whom the audience would automatically think was crazy.
This was Peter Lorre's last film for Warner Bros.
Luis Buñuel wrote in his autobiography ("My Last Sigh"), he was employed by Warner Bros. and submitted a story idea for a horror movie about a disembodied hand.
Though called "Bruce Conrad" in the script, Robert Alda is billed as "Conrad Ryler"; Charles Dingle is billed as "Raymond Arlington"; Ray Walker is billed as "Mr. Miller".
Curt Siodmack was under contract to Universal Pictures and,unfortunately, the then head of Universal, Robert Arthur, was not that fond of horror movies otherwise this picture would have undoubtedly been made there. When Arthur realized how very successful both critically and financially horror movies are he quickly brought them back to Universal. Patricia White, who married the great playwright Philip Barry and started using her married name went on to sign a long dual movie contract with both M.G.M. and Universal Studios.