A gorilla 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 gorilla, and the animal is holding out a twenty-dollar bill. Well, now the bartender is just at a loss for words. He can't believe that a gorilla walked into his bar, ordered a martini, and then actually had a twenty-dollar bill to pay for it.
So, in amazement, he takes the twenty and walks to the cash register to make the change. While he's standing in front of the cash register he stops for a second and thinks to himself, "Let me try something here and see if the gorilla notices anything."
So he walks back over to the gorilla and hands him a dollar change. The gorilla doesn't say anything, he just sits there sipping the martini. After a few minutes the bartender just can't take it anymore.