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* ActorSharedBackground: Creator/HumphreyBogart owned his own boat, called the Santana (which was later the name of his production company), and was an expert at handling it, including competing with it in races.
* CastTheRunnerUp: Dan Seymour signed up to play as a Cuban revolutionary and was shocked to notice his character wasn't in the script. Instead, he was given the role of Capitaine Renard.
* CreatorBreakdown: Due to Creator/HumphreyBogart's affair with Creator/LaurenBacall, his marital problems escalated during filming, and his drinking often resulted in his being unable to work. They got married three months after filming wrapped.
* CreatorChosenCasting: Creator/HumphreyBogart was always the first choice for Harry Morgan.
* CreatorPreferredAdaptation: Creator/ErnestHemingway didn't think much of the novel, and called the movie an improvement. The film diverges wildly from the book's story after the first few chapters.
* DarkhorseCasting: At the time of casting, Creator/LaurenBacall was an 18-year-old model. She appeared on the cover of ''Harper's Bazaar'', and was noticed by Creator/HowardHawks' wife, Nancy "Slim" Keith, who showed the cover photo to her husband. Hawks sought Bacall out in April 1943 and signed her for the role, her first movie appearance.
* DyeingForYourArt: The 300 pound Dan Seymour was told to gain weight for Capitaine Renard.
* EnforcedMethodActing: A friend of Walter Brennan (Eddie) suggested to put a rock in his shoe to simulate a limp. It went over so well that it became a trademark of sorts.
* FollowTheLeader: Though it's distinct on its own, the movie shares more than a few similarities with ''Film/{{Casablanca}}'', even some of the same cast members (Bogart, Dalio and Seymour).
* IronyAsSheIsCast: Creator/HumphreyBogart, who in real life was a notorious drinker, playing the relatively sober character.
* NamedLikeMyName: Protagonist Creator/HarryMorgan. Ironically, the actor was born Harry Bratsberg, and started his film career under the name ''Henry'' Morgan (not to be confused with the 17th century Welsh privateer), only to later change it to [[RenamedToAvoidAssociation avoid confusion]] with a popular American humorist of the time.
* NonSingingVoice: Averted; though an urban legend sprang up that Andy Williams dubbed Creator/LaurenBacall's singing voice, it turns out Bacall did her own singing.
* RomanceOnTheSet: Creator/HumphreyBogart and Creator/LaurenBacall fell in love during production. Creator/HowardHawks afterward said that it was actually Bacall's character Marie that Bogart had fallen for, "so she had to keep playing it the rest of her life." Considering that Hawks crushed on Bacall himself, [[UnreliableNarrator and was known for his tall tales]], it must be taken with a grain of salt.
* StarMakingRole: For Creator/LaurenBacall.
* ThoseTwoActors: The fist of four movies that Creator/HumphreyBogart and Creator/LaurenBacall made together.
* ThrowItIn: Most of the dialogue was improvised by the cast.
* UnderageCasting: Creator/LaurenBacall was 19, yet her character was 22.
* WhatCouldHaveBeen: Creator/AnnSheridan was considered for the part of Sylvia/Helen when her character had a larger role in the film. When the role became smaller, Dolores Moran was cast as a more voluptuous contrast to slender Creator/LaurenBacall.
* WriteWhoYouKnow: Marie was based on Hawks' real-life wife at the time, including her nickname "Slim".
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