Do sloths fart? Until recently, a confident answer appeared in books, articles and even conservation explainers: no. Then a baby Hoffmann's two-toed sloth sat in a warm bath, released a stream of bubbles and turned a wonderfully silly question into a useful lesson about how science changes.
The safest answer now is yes, at least some sloths can pass intestinal gas. That does not mean every sloth species does it often, or that every detail of the older explanation was wrong. It means a real observation has overturned the strongest version of the no-fart claim.
What did the video actually show?
In July 2025, Live Science reported what was described as likely the first footage of a farting sloth. The animal was a baby Hoffmann's two-toed sloth, scientifically known as Choloepus hoffmanni, in a bucket of water. Bubbles made the normally invisible event rather difficult to misinterpret.
Zoologist Lucy Cooke shared the clip with wildlife veterinarian Andrés Sáenz Bräutigam, who has worked with sloths for more than a decade in Costa Rica. Bräutigam told Live Science that sloths can be very gassy and that warm water can help a sloth release gas and pass waste.
It is an excellent observation, but it is not a controlled experiment or a survey of all sloths. It shows that this individual could fart. It does not yet tell us how common the behaviour is, whether it differs between two-toed and three-toed sloths, or how much fermentation gas leaves by this route.
Why did people think sloths could not fart?
The older explanation began with genuine and unusual anatomy. Sloths eat a leafy diet that is hard to break down. Microbes in their digestive system ferment plant material, a slow process that produces gas as well as making nutrients available.
The Sloth Conservation Foundation's detailed guide to sloth digestion describes a large, multi-chambered stomach and a looped oesophagus that helps keep food in place while the animal hangs upside down. It also presents the traditional account that sloths cannot vomit, burp or fart, with fermentation gases instead diffusing into the bloodstream and leaving through the lungs or skin.
A published anatomical study of brown-throated three-toed sloths, available through PubMed, confirms just how specialised the sloth stomach is. The researchers described multiple compartments and folds suited to a fermenting herbivore. This anatomy makes the old gas explanation plausible, but anatomy alone cannot prove that no gas ever travels through the intestines and out of the body.
So was the old explanation completely wrong?
Not necessarily. Gas can leave an animal by more than one route. The video proves that rectal release is possible in at least one Hoffmann's two-toed sloth. It does not prove that absorption into the blood and release through the lungs never happens. Both routes could operate, perhaps in different proportions depending on the animal, meal, gut microbes or physical conditions.
There is also a species caution. The stomach study examined brown-throated three-toed sloths, while the bubbling baby was a two-toed sloth. The two families share a slow, fermentative approach to digestion, but they are not interchangeable. A neat answer for “sloths” can hide meaningful differences between species.
This is why the best correction is modest: the blanket statement “sloths do not fart” is no longer safe. We need more observation before replacing it with another sweeping claim.
Why are sloths so full of gas?
Leaves are tough packages of cellulose with relatively little readily available energy. Sloths cannot unlock that food on their own, so communities of gut microbes do much of the chemical work. Fermentation takes time and creates gases such as methane and carbon dioxide.
A sloth's slow metabolism and long digestive journey mean that food remains in the system for an unusually long time. Gas is not simply a joke in rescue and veterinary care. Bräutigam explained that it can show up on X-rays, interfere with ultrasound images and become a concern when pressure builds.
Diet matters too. Wild sloths choose leaves from familiar trees, while rescued or captive animals may receive vegetables and other foods. Easier-to-ferment foods can encourage gut microbes to produce gas quickly. That is one reason specialist carers are careful about feeding. A sloth should never be offered human snacks just because it appears interested.
What can one funny video teach us about science?
Science is not a collection of facts carved in stone. It is a method for building the best explanation from available evidence, then revising that explanation when something new appears. Sometimes the new evidence is a fossil, a genome or years of tracking data. Sometimes it is a baby sloth making bubbles in a bath.
The episode also rewards precise language. “No one had clearly documented a sloth fart” would have been easier to update than “sloths cannot fart.” The first statement describes the evidence. The second turns missing evidence into a biological impossibility.
There is plenty left to learn. Researchers could compare species, measure how often gas follows different routes, examine the effects of diet and explore whether warm water changes gut movement. Until then, the honest answer is also the memorable one: yes, a sloth has been filmed farting, and that tiny puff of evidence was enough to improve the story.
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