The Octopus and Its Three Hearts

The octopus is a soft animal that lives in the sea. It has eight arms and no bones. But the most surprising thing is inside its body. The octopus has three hearts, not one.

Two of the hearts push blood to the gills. There the blood takes in oxygen from the water. The third heart then sends this blood to the rest of the body, so the octopus has energy to move.

The blood of an octopus is blue, not red. It is blue because it has copper inside. This special blood helps the octopus live in cold, deep water. When the octopus swims, its main heart stops, so it likes to walk on the sea floor instead.