Who among us has not wondered if a snake can fart?
Dani Rabiotti, a quantitative ecologist, asked this question on Twitter in 2017. Her research on animal gases went viral, of course. From there, #doesitfart quickly spread (like a, well, you know). Rabiotti and her co-author Nick Caruso turned the topic into a book that arrived in 2018 New York Times Best seller list.
Simply put, a fart is “any gas expelled from an animal’s bottom that is in front of its mouth,” Rabaiotti and Caruso explain in their seminal book. Do You Fart?: The Ultimate Field Guide to Animal Farting.
An animal’s fart can come through its anus, if it has one, or its cloaca—a combined opening for urination and defecation. The release of gas causes the hole to vibrate against an organism’s sphincter muscles, creating a sound.
What animals can fart?
Many animals can and do fart. Humans, of course, but so do hyenas, manatees, dogs and cats. Quite a few creatures you might not expect will also be added to the chorus. As mentioned above, there are enough inflatable animals to fill a book.
Consider herring, for one. Not only can fish fart, but they do it on purpose to communicate. Herring fart at a frequency too high for predatory fish to hear, so their farts act as a secret fish code.
Farts are not all created equal and they can serve different purposes. Passage of gas can relieve intestinal discomfort or be used to communicate, as with the herring above. Farts can also be used to scare off potential predators. When threatened, a Sonoran coral snake sucks air into its cloaca (the one hole snakes use to urinate and defecate) and exhales it again with a hissing noise. Rabiotti and Caruso write that this “cloacal explosion” sounds like a “higher, shorter version of a human fart.” Keep this in mind the next time you’re hiking in and around southern Arizona.
The Bolson Pupfish, which lives only in Mexico’s Cuatro Cienegas Reserve, has the distinguished distinction of being an animal that must fart to live. Fish feast on algae, which produce gas. As gas builds up in the fish, it begins to swim to the surface, where hungry predators await. The fart allows the fish to sink back into the sediment it normally rests on.
In addition to being able to survive absolutely anywhere, American cockroaches can also fart.
What animals can’t fart?
Some animals can fart, but don’t, while others are really incompetent.
Bats, while they should be able to fart, don’t seem to. Perhaps this is because they digest their food so quickly, preventing the build-up of internal gas. Most animals that digest their food theoretically have the ability to fart, although they may not do so loudly or often.
Animals that cannot truly fart lack a digestive system to break down food in a way that creates gas within an enclosed space (like the intestines) and then expels it. A Portuguese warrior, for example, is unable to drink. Technically a colony of specialized organisms, the o’war man liquefies the prey it catches in its tentacles.
Birds generally don’t fart, Rabiotti and Caruso explain, because the food they eat goes through their digestive system very quickly (no time for gas to build up) and their gut microbes are different (and less gas-producing ) than mammals. The jury is out on whether amphibians got this. Frogs’ sphincter muscles are not very strong, making it less likely that the passage of any gas would cause vibrations strong enough to be audible.
A most unusual among mammals, sloths do not fart. They digest their simple food extremely slowly, and while their gut microbiome produces methane, that gas is absorbed and exhaled, not released as flatulence.
This story is part of Popular Science’s Ask Us Anything series, where we answer your weirdest, most mind-boggling questions, from the mundane to the outlandish. Got something you always wanted to know? Ask us.