A man hears a knock at the door and opens it. There is nobody there. He looks down and sees a snail on the doorstep. He picks it up and throws it out into the yard.
About three years later he gets another knock at the door. He opens it, there is nobody there. He looks down and sees a snail on the doorstep. The snail looks up at him and says, “what the hell was that all about???”