During the late 1800's as the U.S. was expanding westward, a traveller stopped off in a mid-western tavern for a meal and a drink.
Upon entering the tavern, he orders a steak, potato and an ale. He sits eating his meal quitely and as he finishes he notices a large jar of money sitting at the end of the bar. When the bartender comes to collect his plate he asks, "What is that large jar of money for?" To which the bartender replys, "It is a local bet that I have running."
The traveler asks if he would be willing to let him in on the bet and the bartender tells him that if he can make his mule laugh the traveler can have the jar of money, else he has to add $10 to the jar.
The traveler says, "I can make your old mule laugh, so I'll take that bet." With that he tosses $10 into the jar and the bartender tells him to wait out front for him.
After a few minutes the bartender brings the mule around and the traveler walks up and whispers something in the mules ear. At this point the mule starts laughing hysterically. The bartender is quite surprised, but hands over the large jar of money. The traveler thanks the bartender, pays for his meal then hits the road.
Well, some number of years later the traveler passes through this town again. Remembering the tavern he stops off to eat and drink. Again there is a large jar of money on the bar. So the traveler asks, "So what is the bet this time?" The bartender tells him that if he can make the mule cry, he can have the jar of money or pay $10 for failure.
"I'll take that bet!" says the traveler and he drops his $10 into the jar. "Do you mind if I have just a minute out back with your mule? I promise not to hurt him and will bring him around front in just a few minutes."
The bartender thinks about it for a moment, but agrees and steps out front to wait on the traveler. A few minutes later, the traveler brings the old mule around to the front of the tavern and it is crying like a widow at a funeral.
The bartender is just about to pay up when he asks, "Last time I didn't ask what you said to make the mule laugh, but this is twice you've beat me and I must know what you said or did to my mule."
The traveler tells him that the first time he told the old mule his penis was bigger, this time he showed him.