One day, little Billy comes home from kindergarten...

One day, little Billy comes home from kindergarten for lunch. Not finding his mother in the kitchen, or the living room, he heads upstairs to check her bedroom. He opens the door, and what does he see, but his father, who had also come home for lunch, stripped naked, on top of his mother, also naked, heavily into the act of lovemaking. Not wanting to traumatize the boy, the parents continue as if nothing was wrong. Billy watches, and after a couple of minutes asks,"Daddy, can I climb on and have a horsie ride?" "Of course, Son, we're a family." So Billy climbs on and after a few more minutes his mother starts moaning and writhing wildly. "Hang on Dad!", cries Billy, "this is where me and the mailman usually falls off!"