I didn't grab my camera fast enough this afternoon. JC was sharpening his claws on his chair (an old, heavily upholstered dining room chair where it's allowed), and, without stopping, leaned his head back and scratched behind his ear with a back paw. His front paws were slowly shredding, while his back paw was moving rather fast. I've never seen anything like it. My husband says he's seen him do that at least twice while using his cat tree.