At the weekly comedy show at Kabin, an East Village bar, the last performer, Dan St. Germain, asked, "Did all of you fart at once? You're a great audience, but this place smells terrible! Did you make a deal with the comics: 'We'll laugh at everything, if you just let us shit our pants?'"
I have no sense of smell, but he was probably right. The back room of Kabin lacks ventilation, and probably people do fart more while laughing. Both emissions — laughter and gas — are convulsive & cleansing. A laughing audience is a flatulent one.