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Why does an octopus need three hearts when you need only one?

The answer starts with a challenge: getting oxygen around its soft body.

Water flows over two gills tucked inside its muscular mantle.

Beside those gills sit two small pumps, called the branchial hearts.

Each pushes oxygen-poor blood through one gill to collect oxygen.

The third heart, the systemic heart, sends oxygen-rich blood throughout the body.

So two hearts serve the gills, while one supplies everything else.

That includes eight busy arms, reaching, gripping, and exploring the seafloor.

Another surprise: that blood turns blue when carrying oxygen.

Its oxygen-carrying protein, hemocyanin, uses copper instead of the iron ours uses.

That chemistry can work well in cold water with little oxygen.

But swimming brings a catch: the main heart can briefly stop.

Crawling generally costs less energy, making it a handy everyday option.

Three hearts, one mission: keeping oxygen flowing through an extraordinary body.