"Spellbound" has one of Hitchcock's finest casts, with Gregory Peck and Ingrid Bergman in the lead roles, and legendary Russian actor Michael Chekhov and Hitchcock favorite Leo G. Carroll in support. But as ever, it could have turned out very differently: Selznick originally wanted Joseph Cotten, Dorothy McGuire ("Gentlemen's Agreement") and Paul Lukas ("Watch On The Rhine," "20,000 Leagues Under The Sea") for the lead roles, while at one point he thought about luring Greta Garbo out of retirement to play Dr. Petersen. Peck, Bergman and Chekhov won out, although Cotten would eventually get the chance to play the role, taking on Dr. Edwardes/John Ballantyne in two separate radio productions in 1948 and 1951.
Selznick had given Hitchcock his first Hollywood break with "Rebecca" in 1940, and they'd had a huge Oscar-winning success with it, but the producer had mostly lent the director out to other studios since, for the likes of "Suspicion" and "Shadow of a Doubt." "Spellbound" marked their first collaboration since "Rebecca," and things went less smoothly, with the director and producer clashing, as we've seen, on everything from casting to the Dali sequence. As a result, relationships became estranged, and it may have contributed to the following year's "Notorious" being sold off to RKO Radio Pictures, in part because Selznick needed cash after overruns on "Duel In The Sun" (which Selznick must have regretted: Hitchcock's film became a giant hit). In 1947, they would make one final film together, the poorly-received "The Paradine Case," but Hitchcock had become too powerful, the partnership had unravelled, and the director and producer never worked together again.
The sound of the theremin, which had been invented in 1928, would become associated indelibly with science fiction thanks to its use in films like "The Day The Earth Stood Still." But the instrument originally got its start in Hollywood (it had been used in the scores to some Russian films like 1931's "Odna") thanks to the score for "Spellbound." After Bernard Hermann turned the project down, Hungarian composer Miklós Rózsa ("The Four Feathers," "Ben-Hur") got the gig, and decided to use the eerie instrument as the centrepiece of his score. It was played by Dr. Samuel Hoffman, a medical doctor who had a sideline as one of the most important practicioners of the instrument, later playing on the scores for "The Thing From Another World," "It Came From Outer Space," "The 5000 Fingers Of Dr. T" and "The Ten Commandments," among many others. The score would win an Oscar, and remains one of the composer's favorites, but Hitchcock never liked it, saying it got in the way of his direction.