If you think about it, cats use scratching posts (or other objects ) to pull off the sheath off their front claws, as well as stretch muscles. Hind claws are a whole different ballgame! I've noticed that the older my cats get, the thicker some hind claws can get, and they often need trimming too. Are you maybe just jealous that you can't chew your toenails lol? (Just kidding)