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September 26, 2026 Fact of the Day Mammals Sloth and human hands work the opposite way. By Nicole Villeneuve In a relaxed state, human hands are most likely to have uncurled fingers, while a clenched fist usually signals tension. But it’s the opposite for sloths: Their hands naturally curl into a hooklike grip, a useful adaptation for an animal that spends about 90% of its life hanging upside down from branches. Sloth hands are built to grab hold, with long, curved claws and specialized flexor tendons that help keep their unique digits curled around branches without much muscular effort. To let go, however, a sloth has to actively extend its fingers, using muscle energy to stretch through the natural pull of the flexors. How else do animals live in trees without falling? Fact Reveal Squirrels use their ___ to help them steer and balance as they run along narrow branches. See the Answer Keep Exploring Reptiles Why Do Iguanas Fall From Trees? Mammals Animals That Walk on Their Knuckles Mammals Why Are Sloths So Slow? Was this email forwarded to you? Sign Up Advertise Contact Us Privacy Policy Terms of Use 325 North LaSalle Street, Suite 200, Chicago, IL 60654 If you'd like to unsubscribe from all Animal Facts emails, click here.