OK, here's the deal: don't do this. It's a really great way to get infected with all kinds of nasty things.
Also, it's kinda gross. Also, I doubt any of you are in the sheep-raising business, so there's really no need for you to go using your teeth to castrate anything, unless you're just one of those people who likes to do sick and sickness-inducing things.
So, what could possibly be so awful that I put it behind a cut while this is visible? And what could this possibly have to do with Christmas?
Reindeer, my friends. Reindeer are all about Christmas. You see, male reindeer loose their antlers in winter. HOWEVER, female reindeer (or castrated males) keep theirs. You'll notice all your pictures of Santa and his sleigh feature reindeer with antlers.
Don't think about it too much.