This is an old riddle that I remember from when I was in school. My science teacher asked us this one and it quickly stumped the class. I remember how excited I was when I finally figured it out! This puzzler has been around for a long time so some people may know the answer right away. I was suprised by how few people had heard it before. Even the people who remember hearing it, they still could not remember the answer. This is one of my favorites