Old one but good..

A little girl asked her Mom, "Mom, may I take the dog for a walk
around the block? Mom replies, "No, because she is in heat."
"What's that mean?" asked the child. "Go ask your father. I think
he's in the garage." The little girl goes to the garage and says,
"Dad,may I take Belle for a walk around the block? I asked Mom, but
she said Belle was in heat, and to come to you." Dad said, "Bring
Belle over here." He took a rag, soaked it with gasoline, and
scrubbed the dog's backside with it and said, "Okay, you can go
now, but keep Belle on the leash and only go one time around the
block." The little girl left, and returned a few minutes later with
no dog on the leash. Surprised, Dad asked, "Where's Belle?"

( YOUR GONNA LOVE THIS!!!!!!!!! )

The little girl said, "She ran out of gas about halfway down the
block, so another dog is pushing her home."