Little Johnny came in from school and asked if he could take his dog, Molly, for a walk.
"You can't dear, Molly's in heat," said the mother.
"What's heat, Momma?" asked Johnny.
"Your dad is out in the garage. You better go ask him," said Momma.
"Hey Daddy, I want to take Molly for a walk, but Momma says I can't cause she's in heat. What's heat?"
His dad was cleaning his tools in some gasoline. He took a rag, dipped it in the gasoline and rubbed it all over Molly's rear end. "Don't worry about it, son. This will fix her." With that, Little Johnny took Molly for the walk.
About twenty minutes later he returned without the dog. "Where's Molly?" his dad asked.
"She ran out of gas about two blocks away, Daddy," answered Little Johnny, "But don't worry: one of the neighbor's dogs is pushing her home."