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An astoundingly huge and horrible fart; the kind that can clear a room, or even an entire grocery store – a fart from which there is no escape for innocent bystanders.

The act of letting such a fart is to "set loose the Beast from Within."
"Hey, why is everybody leaving?"
"Don't go in there!"
"Why not?"
"Frank just set loose the Beast from Within!"
by HAL 9000 February 26, 2008
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