IF a person has a pink monkey
THEN take a refrigerator
It comes from the excellent book, "Expert Systems: Principles and Programming" by Giarratano and Riley. They use it as an example to make their point about shallow knowledge structure. It made me laugh because it's so silly, yet made their point perfectly clear. I love the book and it's one where you can pick it up and start reading at any point. A great book to read if you're interested in expert rule systems. Plus, they have funny examples that make you think.