From Dr. Michael Eades' blog:

"What if you were terrified of having rats in your house, so you brought in a snake to get rid of them. Unbeknown to you, the snake happened to be pregnant, and next thing you knew, you were overrun with snakes, which you found more frightening than the rats. You took steps to start getting rid of the snakes, but then here came the rats back in full force. Now you want to get rid of both of them."

http://www.proteinpower.com/drmike/?p=680