The octopus's main systemic heart stops beating when it swims, making swimming exhausting for them.

When an octopus swims, its systemic heart actually takes a break and stops beating. This means oxygenated blood doesn’t circulate to the body during swimming, so the octopus quickly gets tired. That’s why octopuses prefer to crawl along the ocean floor using their arms—it’s less tiring. This unique heart function shapes how octopuses move and hunt, favoring quick bursts of energy and camouflage over long swims.