Unknown to Lauren Bacall, Howard Hawks had the option to revert to a partial Jules Furthman script that gave some of Bacall's dialogue to another actress, should the aspiring actress not work out. It wasn't needed. In fact, shooting continued with Faulkner re-writing scenes to spotlight her character.
Lauren Bacall was terrified on the set of her first film. Fortunately, Humphrey Bogart was able to put her at ease with humor and acting tips. Bacall had nervous shakes in her first scenes and quickly learned that keeping her chin down and her eyes up kept her head from trembling. It developed into a trademark sultry look.
At the funeral for her husband, Humphrey Bogart, Lauren Bacall put a whistle in his coffin. It was a reference to the famous line in the film where she says to him: "You know how to whistle, don't you Steve? You just put your lips together and blow."
Howard Hawks gave John Huston the climax (a shootout on a boat) that he was unable to fit into the end of this film. Huston used this in Paixões em Fúria (1948), as he had been having difficulties coming up with a satisfactory ending.
The most famous scene in the film is undoubtedly the "you know how to whistle" dialog sequence. It was not written by Ernest Hemingway, Jules Furthman, or William Faulkner, but by Howard Hawks. He wrote the scene as a screen test for Bacall with no real intention that it would necessarily end up in the film. The test was shot with Warner Bros. contract player John Ridgely acting opposite Bacall. The Warners staff, of course, agreed to star Bacall in the film based on the test, and Hawks thought the scene was so strong he asked Faulkner to work it into one of his later drafts of the shooting script.