Trivia: The final repetition of the line "He'd kill us if he had the chance" had its inflection changed because preview audiences became preoccupied with questions over whether Harry had misinterpreted the couple's conversation or if they were deliberately being misleading (or both). The ambiguity was initially intended, but appeared to work a little too well and distracted the audience from appreciating the rest of the ending, so this delivery of the line was made more definitive.
Trivia: The dream sequence in which Harry tries to talk to Ann was originally meant to take place in real life (within the film, that is). The production didn't have time to finish the scene and the fog effects looked too phony. But rather than scrap the scene entirely, editor Walter Murch came up with the idea to include the footage as a dream.