The entry on sloths explains that while they eat a lot of plants, they avoid releasing gas through the quirk of their slow digestion. “They only poo about every three weeks,” says Rabaiotti.
If gases accumulated in sloths’ intestines over that long a time, they might get sick — and even burst. So would-be sloth farts are simply reabsorbed through the intestines into the bloodstream. The gases are then respired out of the lungs: literal fart breath.
There are some cases where researchers just don’t know if animals fart or not. Like with salamanders and other amphibians, which “may not possess strong-enough sphincter muscles to create the necessary pressure for a definitive flatus,” the authors write. Gases may ooze out of their bums continually. Is that a fart? Some questions in science are best left to philosophy.