Brains On! Science podcast for kids · Brains On Universe

Totally Slothsome: All about sloths

January 20, 2026·28 min·2 clips

Sloths are the only mammal that doesn't fart, using gas to bob like a buoy in water.

This episode explores the fascinating biology and behavior of sloths, the famously slow tree-dwelling mammals. Host Molly Bloom is joined by co-host and Brains On fan Christina Aru, who also hosts a podcast interviewing young Latinx stars. The show answers listener questions with help from special guests, including zoologist Lucy Cook, founder of the Sloth Appreciation Society. Lucy Cook explains that sloths are slow because they are highly efficient energy conservers, not because they are lazy. Their diet of low-nutrient leaves requires multi-chambered stomachs for slow digestion, and they have extra neck vertebrae to turn their heads instead of moving their bodies. Cook reveals that sloths are the only known mammal that does not fart, and the gas from digestion instead provides buoyancy, making them surprisingly adept swimmers. When swimming, sloths use a "doggy paddle" motion with their arms and can move three times faster in water than they crawl on land. Their long, curved claws allow them to hang effortlessly from branches, and a special muscle mechanism lets them grip tightly even while asleep. Ecologist Jonathan Pauly investigates the mystery of why three-toed sloths make a risky weekly journey to the base of their tree to defecate. Pauly's research uncovers a symbiotic relationship involving sloth moths that live in the sloth's fur; the female moths lay eggs in the sloth's dung, and the resulting moths return to the sloth. The moths' decomposition in the fur fertilizes algae growth, which provides the sloth with green camouflage against predators like harpy eagles. The episode also features a segment called "So You Think You Can Slow-Mo," which humorously highlights other slow animals like koalas, banana slugs, and tortoises. The tone is educational and playful, blending factual explanations with lighthearted skits and character voices to engage young listeners. This episode is perfect for curious kids and families interested in animal science, quirky animal facts, and ecological mysteries. Listeners who prefer fast-paced action or non-biological topics might find the deliberate pace less appealing.

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