Revealing mistake: In the scene where Cary Grant punches Jimmy Stewart: Jimmy starts falling back (and you hear the sound effect of the punch) when Cary's fist is a good 1-2 feet from Jimmy's face.
The Philadelphia Story (1940)
1 revealing mistake
Directed by: George Cukor
Starring: James Stewart, Cary Grant, Katharine Hepburn, Ruth Hussey
Continuity mistake: Uncle Willy pours a glass just over half way full of vodka. With each shot the amount of vodka in the glass changes.
Elizabeth Imbrie: What's this room? I've forgotten my compass.
Macaulay Connor: I'd say, south-by-southwest parlor-by-living-room.
Trivia: Hepburn wanted Clarke Gable and Spencer Tracy for the male roles, but the studio gave her Cary Grant and Jimmy Stewart instead. (She did get Spencer eventually when requested for Woman of the Year).