And they timed the characters' breathing to their dialogue and at the same time let the characters' belly muscles and diaphragm tighten so it would really like they were letting out air while talking.
If you put your thumb here just below your rib cage and you practise breathing in deeply, you should get to the point where you can feel your diaphragm, that's this area here pushing out against your thumb.
And, just as you're about to throw up, the muscles in your abs and diaphragm literally squeeze your stomach, forcing its icky contents back up your digestive tract to your throat and then your mouth.
In hiatal hernia, the stomach and lower part of the esophagus slide up through the esophageal hiatus, which is an orifice in the diaphragm, and this decreases the pressure of the lower esophageal sphincter.
And there may be more to it, because laughter engages your diaphragm, which stimulates the flow of lymph — a fluid that moves your immune cells around the body.