So, apparently Some species of hummingbird (sword-billed hummingbird in the pictures) use their feet for preening since their bills are so long and awkwardly-shaped. That makes me think of how deinonychosaurs might have used their toe claws to preen, almost like a dog. Perhaps therizinosaurs used their hand claws as well? That must've looked funny.
Images from BBC's Life of Birds, The Mastery of Flight.