In the "Rhapsody in Blue" portion of the mammoth "Pretty Girl" number, one of the silver-fringe-and-antlers quartet of dancers gets visibly disoriented when her group does its final moves. She's the second one from the left, and her movements are completely out of sync with the other three until, with a thump, she sits down on the stairs. Since the incredibly complex number was shot in very long takes, the error was allowed to remain in the film.