Getting A Cake_英语笑话

little johnny walked into the kitchen, saw his mother making a cake and announced, "i'll be playing in my room for the next two hours. i sure would like a piece of cake when you're finished."
later, when his mother brought him a piece of cooled cake, little johnny exclaimed, "golly, it worked!"
puzzled, his mother asked, "what do you mean?"
little johnny replied, "daddy said that in order to get a piece around here, you have to spend a couple of hours playing first!"