When our son Jonathan was a toddler, I would keep him home with me sometimes instead of taking him to his babysitter. On one occasion, I was eating lunch at the living room coffee table and Jonathan was playing on the floor in front of me. He’d waddle over occasionally to beg for a bite of what I was eating. I’d give him something to eat, and he’d waddle off again to play. On one of his trips back, he stopped in front of the coffee table, and was waiting for his next serving. But as I cut up something for him, he grew impatient and reached out to grab it for himself. Instead of grabbing the food I was cutting up, however, he grabbed the blade of the knife.