Boy and girl playing (bit rude)

A boy and a girl, are playing in the sandbox.

Unexpectedly, the 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 boy rolls up the hill, he finds himself upside down against a tree.

He groggily gets to his feet, runs over to where the girl is out cold, flat on her back, spread eagle.

He lifts up her dress, peeks underneath, and loudly exclaims: "Just what I thought,

Spoiler:

dual exhaust."