Dr. Werhner von Braun was given a public lecture about the earth, and outter space, and so on. Afterwords, a little old lady comes up and tells him that he didn't fool her. She knows the earth don't go around the sun, but it rests on the back of a giant turtle.
"Really?" teased the amused von Braun. "and what does the turtle stand on?"
"Another turtle."
"Oh? And what does he stand on?"
The little old lady waved a grandmotherly finger at him. "Ah,ah,ah,Doctor,you can't trick me. Everybody knows it's turtles all the way to the bottom!"
My thermodynamics lecturer told that one once. It was elephants though, but I thought Turtles was a bit more modern. The lecture was on entropy.