Yeah. Sounds weird cause it is.
When they work in your abdomen, they inflate it like a balloon, so there's more room. When they close you up, they can't get all the extra air out, so some is left behind. Until it works its way into the blood and then out of the body, it puts pressure on your phrenic nerve, which is located on your diaphragm but extends to the shoulders. So they hurt a lot until you manage to get the gas out.
Also, don't laugh, cough, bend, or have a 20-pound cat jump on your stomach.