This 1951 musical is tonight’s selection as one of “The Essentials,” as chosen by guest co-host Brad Bird – whose taste, this season, has been impeccable. And tonight, there’s the amazing extended ballet ending to An American in Paris, one of the high watermarks of movie musical history. Gene Kelly stars – and in that finale, gets to embody one classic painting after another, and not only bring them to life, but bring them to dance.