A guy hears a knock at his door. When he answers it, there’s nobody there, but there’s a snail on the welcome mat. Frustrated, the guy picks up the snail and hurls it into the street.

Five years go by, and there’s another knock at the door. The man answers it, and again there’s no one standing there, but there’s a snail on the welcome mat.

The snail looks up and says, “What the heck was that all about?”