In a scene early in the film, Anna is seen walking through an open-air market. While this scene was being filmed, an airplane passed over the set, creating a low hum on the soundtrack. Composer Bernard Herrmann was instructed to compose an accompanying score that would obscure the airplane motor. He used low gongs.
While most of the Caucasian actors playing Asians in this film wore dark make-up, Gale Sondergaard was allergic to the make-up being used. Instead, through several weeks of cautious sunbathing, she acquired a deep enough tan to compensate.
Rex Harrison was appalled at the studio's lack of interest in the film and how unhelpful 'Darryl F. Zanuck was to him. He recalled - "This lackadaisical attitude was not at all what I'd expected and I began feeling pretty desperate. Everything was so slow; I wasn't geared to relaxing around pools and drinking all day. I'd been used all my life to working hard, and now suddenly I was in a hot bath, growing weaker and weaker. The sets were only just being constructed, so there was no hope of beginning for weeks, and in the meantime there was nobody I could talk to constructively about how I was to tackle this frightfully difficult role, for which I was far too young and two feet too tall."
Rex Harrison thoroughly enjoyed co-starring with Irene Dunne. He thought her "an excellent actress" and was pleased that she had the confidence to follow her own instincts. He recalled, "She too went her own way and tactfully used the director, as I later learned to do myself, to her own advantage; she listened to what he had to give, and discarded it or used it, as she wished."
When Rex Harrison met John Cromwell, he found him pleasant enough, but rather aloof. "At least two months passed before the production began," recalled Harrison in his 1975 autobiography Rex, "during which time, if we did come across each other, [Cromwell] withdrew, either physically or mentally; I was never able to sit down with him and discuss my fears and worries about playing an Oriental, and he never told me what he thought about the character."
Rex Harrison and John Cromwell had a disagreement over what accent the actor used. Harrison used an Asian accent, while the director wanted him to speak in his normal voice. The conflict over the matter was such that Harrison had to get studio head Darryl F. Zanuck to intervene on his behalf and back him up. To his surprise and delight, Zanuck supported him. However, it ended up causing a rift with Cromwell. According to Harrison, the director didn't speak to him again afterwards.
The real teacher's name was Anna Leonowens. In the film it is changed to simply Owens. But, in the film, on Anna's trunk are three embossed initials, "A L O" perhaps to preserve the real character's name.
The sets for Anna and the King of Siam were some of the most elaborate ever built at Twentieth Century-Fox. Exquisitely detailed and painstakingly constructed, the expensive sets ended up covering several acres of the studio's backlot. According to a Time magazine article dated June 24, 1946, the film was "one of the first postwar productions to splurge on lavish, prewar-style props," which was shot "over five acres of lot covered with $300,000 worth...of Oriental rococo background. Notable eye-filling items: the King's four gold-and-diamond crowns ($84,000) and 23 silk-and-brocade costumes ($23,000);" along with "a coronation scene costing $80,000."
Rex Harrison called producer Louis D. Lighton "a highly intelligent man who had difficulty in articulating his thoughts. He talked in riddles, so abstruse that I used to sit in his office and try in vain to make out their meaning."
The trivia item below may give away important plot points.
In the film, Linda Darnell's character dies by being burned at the stake. This was a particularly difficult sequence for her to film, as she was terrified of fire. What makes this a double irony is the fact that, 19 years later, she was killed in a house fire.