Bette Davis and Mary Astor thought the original script was not very good. They ended up doing massive rewrites on the script themselves.
At Mary Astor's suggestion, her hair was cut into a shingle-bob, because rolling and styling it took too long. She then wore it the same, but a bit longer, in The Maltese Falcon (1941), causing a fashion craze.
When Pete returns from seeing his lawyer, he finds Sandra's agent in the living room listening to her latest recording. This is an excerpt from the first movement of the Piano Concerto No 4 in D minor by Anton Rubinstein, a great rarity and certainly not recorded by anyone else in 1941. It possibly was chosen by Max Steiner because it was no longer in copyright, but whatever the reason, it was a most unusual and sophisticated choice.
Mary Astor mimed playing the piano in this film extremely convincingly, being an accomplished pianist in her own right. However, the piano playing on the soundtrack was dubbed by Max Rabinowitz. When closeups were required, Norma Drury's hands are those seen on the piano.