Biting claws?

One of my recently adopted cats, Harry, just was washing himself in front of me for the first time. While he was washing one of his back feet, I saw him do something which I don't think I've ever seen a cat do before.

He bit at his claws. I was close enough to hear the "crunch" as he did it. Weird. Anybody have cats that bite/crunch their claws? Any idea why they do it?

Here's a pic of Harry biting his claws:

Great picture to capture Harry trimming his claws! Serenity does this! She's so funny! When she gets her weekly manicure, she only ever needs her front claws trimmed, she keeps her back ones trimmed all on her own! Aren't they so smart!

It's easier for cats to take the outer sheaths off their front claws - they scratch on things. For back claws cats often chew to get that loose.
Out door cats and ferals are able to take care of back claws with tree climbing or climbing other surfaces that would wear and remove that.

milo does this too! i keep a check on his claws but he does keep them beautifully trimmed!

Ollie nibbles his toes too! He wears soft paws on his front feet, so sometimes he chews them off when they're close to falling off on their own and he chomps on his back toes to get the sheaths off... I always take a peek at his piggers when I'm holding him and gently pull off any easily removed sheath that's hangin around or any soft paws that are due to fall off (of course I dont tug on anything that causes pain! Just stuff that's pretty much ready to fall off)

Sneakers also bites and pulls on her claws to sharpen them. I thought it was weird when I first saw it because my previous cat never did that!

Bentley does that! I always thought it was wierd because of my four, he's the only claw biter.