A few years ago, a friend if mine leant me a book and I thoroughly enjoyed it. It was a whole series, but I was never able to read the whole series. The first book was about a boy who wasn't wanted by his people so he ran away and he ends up befriending a big hairy creature. As they travel they end up in a swamp and encounter these little hairy creatures that start to devour the big creature. In order to save the boy he puts him in a tree and sacrifices himself. The little creatures leave only a tooth behind.