As the father of a nine-month-old baby, I've learned that getting slapped and scratched in my face and having my hair pulled by the baby is par for the course. But I've also learned that baby has a black belt in Baby Fu! [Insert sound of gong here.]
I'll be feeding her milk and, with her left hand, she'll grasp my left thumb. Probing for the most sensitive area of muscle and nerve, she'll begin thrusting her thumb into mine. But it's not just her thumb that's digging; it's her sharp thumbnail that's going deeper and deeper. Add to the fact that she's flexing that thumb back and forth and back and forth, and Daddy begins to go "Aaaarrrrghhhh!" :)
Baby Fu. Man, even thinking about it hurts.