... Susan Sarandon's breast.
Back up to the previous photo to get some idea of what inspired Kate, the I'll-just-wear-a-black-bra-with-my-white-tuxedo look Susan chose from the SAG Awards.
Don't stoop to the obvious "sag" joke. You're better than that. And Susan is better than that. Feel free to marvel at Susan's amazing daughter, Eva Amurri.