A man walks into a bar with an alligator under his arm.
"This is the world's tamest alligator," says the man, "and I'll prove it." He then throws a tennis ball under a table, and the alligator promptly fetches it.
"Anyone else want to try?" says the man.
"Sure," says the bartender, "but please throw the ball on top of the table, as my knees are bad and I have trouble picking up objects from the floor."
The two men discuss their various health problems for some time, and forget all about the alligator.