finally they admited

Little Johnny, Billy and Tommy were walking home from school one warm
spring day. As they were cutting through the alleys and backyards, they
happened to look through a hole in the fence of one of the yards where
a woman was sunbathing in the nude.

As they looked through the hole, Johnny suddenly started to scream, left his friends and took off running for home.

The next day, as the three boys came home again, they found the
same hole in the fence and started to watch the woman. Again, after
just a few minutes, Johnney started screaming and ran off quickly.

On the third day, the boys were peeping into the hole in the fence
again after school, when Johnny turned around and started to run again.
But this time, Bill and Tommy grabbed him and demanded to know what was
wrong.

Johnny replied, "My mother told me that if I ever looked at a naked woman, I would turn to stone...

And I started to feel a part of me getting awfully hard??? "