Guy looks over and watches another man who repetedly shakes with laughter and smiles a lot. Then every now and then he seems him shake his head and wave his hand back and forth. After watching him for quite some time he walks over to the man and says, "I've been watching you for about an hour now, and I have to ask what on earth are you doing?" The man says, "I've been telling myself jokes." The guy asks, " Then what was going on when you were shaking your head and waving your hand back and forth?" "Oh those are the ones I had already heard."