"We started out doing kindergarten-style things, like putting our hand against our arm and hands, and stuff like that," Kiser says. The classic technique matched on screen ("especially for airy farts," the engineer notes) and allowed the crew to focus on the performance of the fart. Kiser supplemented the vocal noises with real recordings of gastrointestinal activity, picked up by stethoscope microphones. A local Mongolian hot pot joint provided the indigestion.
"Daniel Shiner has the loudest intestinal or digestive system I've ever heard," Kiser notes. "He might have 1% body fat. I think his body, there's no fat to deaden any of the sound."
All the bottom burping ultimately needed to strike the right balance. They couldn't be cartoonish, Kiser says, but they also needed to spurt and sputter to sell them as farts occurring in real time. That meant fielding new fart requests from Kwan and Scheinert as they pieced together the movie.
"I'd get a phone call from Daniel Scheinert, who'd be like, 'Hey, buddy, what's going on?' We really need a fart that sounds like [BRRRRUUUUH].' I'd be like, 'OK, cool, do you want it intestinal? Do you want it inside, or do you need more flat butt cheek?" Then he'd be like, 'Hmm. Interesting. Maybe we'd start with more intestinal, then get butt flap.' These are things we can say in our industry, and it's OK."