Let's Face The Music And Dance

What a pleasure to watch.  Fred Astaire and Ginger Rogers from Follow The Fleet (1936).  The song was composed by Irving Berlin for the film.  The clip below supplies the full set up and context for the song and dance which THC found quite surprising.  It's worth watching the whole thing (and you'll see young Lucille Ball looking over Fred's right shoulder in the opening sequence) but if you want to start when Ginger Rogers makes her first appearance go to 2:30.  THC doesn't know much about dancing technique but thinks anyone with a heart will find the nearly three minute sequence with no cuts to be breathtaking, beautiful and moving.  Along with Fred & Ginger notice the third character, Ginger's dress and the legs it encases.  How did they do that?