Hyssop is a magic user and he adapted a spell that had killed everyone else who'd used it prior. It came very close to killing him as well, but it just missed cutting his head completely in half. The magic adapted afterward and left his mouth permanently split like that.

Thanks! Sometimes I go into fits of babbling about my characters in the artist comment on dA or when I post sketches in my LJ. And I've answered people's questions in the comments on dA too. That's it though.