A little boy and a little girl, both about six, are playing in the sandbox.
Unexpectedly, the little boy farted, causing a little sand between his legs to shift.
She notices, and squeals with laughter, "How'd you do that," she asks.
"Easy," he exclaimed, "I just farted."
"Can I try it," she asks?
"Sure," he says, "anybody can do it."
So she strains, and concentrates, and grunts.
Suddenly, there's a terrible explosion, the sides of the sandbox fly off, all the sand flies out.
The little boy rolls up the hill, he finds himself upside down against a tree.
He groggily gets to his feet, runs over to where the little girl is out cold, flat on her back, spread eagle.
He lifts up her dress, peeks underneath, and loudly exclaims, "Just what I thought, dual exhaust."