A six year old little boy and a six year old little girl are sitting and playing in a sand box. The little boy lifts up one buttock and farts noisily, blowing out a puff of sand.
The little girls grins and says, "Hey, can I do that?"
The little boy say, "I don't know, yer just a girl"
So the little girl, not to be out done, lifts a leg and grunts... Nothing.
She closes her eyes in concentration and grunts harder.... nothing.
Finally, she grunts hard and her face turns red with the effort and .. BLATT she farts so loud and hard, all the sand is blown out of the sand box and the little boy is blown up the hill a ways.
He opens his eyes, gets up and shakes himself off... It is then he notices the little girl, still in the sand box and unconcious. He walks over, lifts up her skirt and says...
"That explains it, Dual Exhaust!"