it was nothing

A mother and her young son are taking a walk through the countryside when the son spots a horse with a huge errection raging between its legs.

"Mommy, what is that thing hanging between the horses legs?" he asks
The mother blushes and avoids the question "Oh, erm... that's nothing"

The boy isn't too pleased with this answer though, and a few days later he happens to be walking past the same field again, but this time he's with his dad. Again, the horse has a ginormous errection.

"Daddy, what's that thing between that horses legs there?" the boy asks again.
"That, my son, is his penis"

"Huh. When i asked Mommy she said it was nothing"

"Yeah, but she's been spoiled"