A teacher entered her classroom one Monday morning and found the word "penis" written on the board in tiny letters. She scanned her class's faces looking for guilt, but found none, so she erased it and continued with the day's lessons. On Tuesday she found the same word written in larger letters. Again, she searched in vain to find the culprit. Every day the same word appeared and each day it grew larger. The following Monday she arrived fully expecting a giant version, but instead found a neatly-lettered sentence: "The more you rub it, the bigger it gets!"