A four-year-old boy asked his friend what a penis was. His friend's response was that he did not know and he would ask his dad.
That evening the second boy asked his dad. His dad gladly exposed himself to his son and with his penis in hand said, "Son this is a penis. In fact, if you take a good look you will see this is a perfect penis."
The next day the second five year old boy met the first five year old boy and called him behind a hedge.
The boy exposed himself and said, "This is a penis. In fact, if it were three inches shorter it would be a perfect penis!"