This is footage from the movie “Broadway Rhythm” (1944). The Ross sisters, Aggie, Maggie and Elmira, sing and move in ways that’ll make your average contortionist blush.
Just watch past the minute mark to see the moves begin. And my favorite is at the 2:50 mark. That has to be the most impressive back bend ever.
Good Luck and Good Acrobatics,
P.S. Thanks to Mike for pointing me to this video!