HOW DO IT KNOW?

My friend Margie's favorite joke:

Little Billy Bob was in class and the teacher asked the question, "Now, students, I want you to tell me what you think is the world's most important invention."

She called on little Betty Sue and little Betty Sue said, "I think it's the wheel, because if we didn't have the wheel we couldn't have the other inventions." The teacher said, "That's good, little Betty Sue."

Next, she called on little Jimmy Joe and he answered, "The atomic bomb, because it changed the world forever." The teacher said, "That's good, little Jimmy Joe."

Next, she called on little Billy Bob, and he answered, "The thermos bottle!" The teacher asked, "With all the important inventions in the world, why would you think of a thermos bottle?"

Little Billy Bob answered, "When you want it hot, it's hot and when you want it cold, it's cold--HOW DO IT KNOW?"

As you might have guessed, "How do it know?" comes up as a reply frequently in her family and also in mine.