2 old guys are sitting on a front porch...

Two old men were sitting on a front porch just watching life pass by. Suddenly, a Great Dane walks across their front lawn. The dog stops, lays down, and begins licking itself.
The first old man says, "Boy, I sure wish I could do that
The other old man says, "I don't know. If I were you, I might try petting him first.