Some years ago Bill Cosby did one of his many great comedy routines about his growing up years in Philadelphia.(1) He recalled a snowy winter day, enough snow on the ground for a really good snowball fight. So he and his friends had one.

Now, if you grew up in an area where snowball fights are a common winter occurrence, you will know that there are certain unwritten rules about what is allowed and what is not. For example, you did not put a rock in the center of your snowball, because that could kill somebody; you did not throw solid ice at somebody for the same reason; and you did not throw slushballs at people because that would make them all wet and force them to quit playing and go home. Common rules anywhere in the world for a kids' snowball fight. And those were the rules in effect…