During the Manhattan Project two scientists were working on a circular radio wave -- a long shot, but nobody knew what would be needed to make an atom bomb.

One day, the younger exclaimed, "I have it! I've diagrammed a circular radio wave!" and thrust his paper at the elder scientist.

The old man said, "You young fool! This is nothing! A naught!" and he rolled the paper into a thin tube and thrust it into a pencil sharpener, the shards falling to the floor.

Immediately they were surrounded by a large group of very angry janitors complaining about the mess.

Then a huge explosion happened and a mushroom cloud rose into the air.

And that's what happens every time you get a critical mass at ground zero.