Cat is biting it off his skin?

-My cat was licking adn biting at his butt my brother was going to pet him and notices soemthing. He called my dad and I and told us that my cat ate his flesh. We looked at it and he's right- THE FLESH IS GONE. My cat has a whole(I guess) and there's no blood or anything but,....his skin is gone. WHAT HAPPENED?Who knows? Take your kitty to the vet. The anal glands can actually burst open if they get blocked up. They will literally make a hole through the back end, near the anus. Other than that it would be hard to guess.are u sure it's his skin not his fur?
:O WTF!!! if i find something i'll let you know :S weired