Octopuses Have Three Hearts, and Two Stop When They Swim

Octopuses possess a circulatory system that seems designed by an alien engineer. They have three hearts: two pump blood to the gills, while the third pumps it to the rest of the body. The strangest part comes during movement. When an octopus swims, the heart that supplies the main body actually stops beating. This isn't a minor inconvenience. It means the creature becomes exhausted far faster while swimming than while crawling along the ocean floor. Scientists believe this is why octopuses prefer to stay near the seafloor and move by crawling or changing color to hide, rather than expending energy on sustained swimming. The metabolic cost is simply too high. This quirk likely explains why octopuses are ambush predators rather than active hunters, and why they're found predominantly in rocky habitats where they can remain stationary and hunt passing prey. The three-heart system works brilliantly for their lifestyle on the ocean bottom, but it's a serious liability in open water. It's a striking example of how evolution optimizes creatures for their specific environment, even when that optimization creates what looks like a design flaw in other contexts.