Girl Blackmails Her Brother after He Kills a Duck

There is a great story about a little boy who killed his grandmother's pet duck. He accidentally hit the duck with a rock from his sling-shot. The boy didn't think anybody saw the foul (sorry!) deed, so he buried the duck in the backyard and didn't tell a soul.
Later, the boy found out that his sister had seen it all. And she now had the leverage of his secret and used it. Whenever it was the sister's turn to wash the dishes, take out the garbage, or wash the car, she would whisper in his ear, "Remember the duck." And then the little boy would do whatever his sister should have done.
There is always a limit to that sort of thing. Finally he'd had it. The boy went to his grandmother and, with great fear, confessed what he had done. To his surprise, she hugged him and thanked him. She said, "I was standing at the kitchen sink and saw the whole thing. I forgave you then. I was just wondering when you were going to get tired of your sister's blackmail and come to me."

Steve Brown, Three Free Sins (Howard Books, 2012), p. 110