1. Preventive bite. Hand is bound to betray you eventually. Get it before it gets you. Remember, every hand is capable of naked aggression.
2. Preemptive bite. Hand is ready to do something. Just look at it. You've got to protect yourself, don't you?
3. Keeps gums healthy.
4. Hand less likely poisoned than food.
5. Tastes good.
[From Errol Morris]