Octopuses Have Three Hearts

Octopuses are already famous for being strange, clever, and just a little bit alien-looking, but one of their most surprising features is hidden inside their bodies: they have three hearts. Two of those hearts move blood to the gills, while the third pumps blood to the rest of the body. That means the octopus has a built-in circulatory system that is doing more juggling than the average creature.

This unusual setup helps octopuses survive in their underwater world, where efficient oxygen transport matters a lot. Their blood is also unusual, because it uses a copper-rich protein to carry oxygen instead of the iron-based hemoglobin humans rely on. That is one reason octopus blood appears blue instead of red. When you put all of that together, the octopus starts to feel less like a normal sea animal and more like nature wandered into science fiction for a while.