Tell me about it. I clip my cats’ claws myself. A very few times I clipped a bit too much and they bled... and the cats remember it years later and go almost crazy when I approach that nail now. Hiss, bite, scratch. How does a cat manage to sharpen its REAR claws? I’ve never watched that in action but my tomcat Timmy does just that. Needles in back and he won’t let me touch them without the worst fight.
Climbing things, perhaps? And I notice mine occasionally lay on their sides and rabbit foot or bearhug the scratching post/box. They must get a few good swipes in then.