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 Henreid. The actor declined 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 Henreid instead of Peter Lorre, who the audience would automatically think was crazy.
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.
The Latin phrase engraved on the fireplace mantle, "Nulla Dies Sine Linea," means "No Day Without A Line." In other words, an artist, no matter his genre, should never let a day go by without doing something creative.