A monkey goes into a bar and orders a martini. This totally amazes the bartender, but he thinks, "What the heck, I guess I might as well make the drink." So he mixes the martini. He then walks back over to the give it to the monkey, who is holding out a twenty-dollar bill. Now the bartender is at a loss for words. He can't believe that a monkey walked into his bar, ordered a martini, and then actually had a twenty-dollar bill to pay for it.
In amazement, he takes the twenty and walks to the cash register to make the change. While he's standing in front of the register he stops for a second and thinks to himself, "Let me try something here and see if the monkey notices anything."
So he walks back over and hands him a dollar change. The monkey just sits there sipping the martini. After a few minutes the bartender just can't take it anymore.
"You know," he says, "we don't get too many monkeys in here."
And the monkey says, "At nineteen dollars a drink I'm not surprised."