Bubblegut occurs when excessive air is trapped in a long, shit-filled intestinal tract. It causes the sensation of a pending ass explosion of either air, poo, or a bit of both.
"I shouldn't have had all that coffee after eating chili for lunch. I'm getting major bubblegut..."
When you gotta fart, you got gas, one of two things gonna happen soon...1) you gonna fart or 2) you gonna shit
"Oooh, we better step away from you, you look like your stomach got bubblegut."