Trivia: Fred MacMurray wears his real-life wedding ring throughout the movie. His character in the movie is single.
Trivia: When mom exposes her pretty scary painting to Bruno it very much resembles the key scene in the film "The Picture of Dorian Gray" from 1945.
Trivia: Orson Welles' line "...you know what the fellow said... In Italy for thirty years under the Borgias they had warfare, terror, murder, bloodshed - but they produced Michelangelo, Leonardo da Vinci, and the Renaissance. In Switzerland they had brotherly love, five hundred years of democracy and peace, and what did that produce? The cuckoo clock." was not in the script. Welles just wanted to say it, so he did, much to the anger of the original author. He thought it was a terrible piece of writing but it has turned out to be the most memorable line in the entire film.
Trivia: At the end of the movie Lauren Bacall says to Marlowe "Phil, there's two men out back behind some trees". This is the only time in the movie that she refers to him by his first name. (01:49:45)
Trivia: Leopoldine Konstantin plays Claude Rains' mother in the movie, even though in real life she was only three years older than him.
Trivia: Hitchcock's cameo comes relatively early in the film - he is playing bridge with a man and a woman on the train to Santa Rosa.
Trivia: Joan Fontaine won a Best Actress Academy Award for her role as Lina McLaidlaw Asygarth in this film. This is the only Oscar-winning performance in an Alfred Hitchcock film.
Trivia: Although they played mother and son in this film, Anne Revere was only ten years older than John Garfield.