I don't think its just Mudokins who have bad gas problems. You ever notice all the green gas in the Slig Barracks in the background? I bet sligs have bad gas aswell. Maybe thats just the nature of the creatures and beings of Oddworld. They are all passing gas too much wether its a fart or a belch that makes the air sort of give that greenish yellowish hue color. Thats a lot of gas!