The octopus has three hearts (and one stops when it swims)

Octopus blood isn't red, it's blue: instead of iron it uses copper to carry oxygen, a system that works better in cold, oxygen-poor water. But the trick has a price — it's less efficient, so the octopus needs three hearts to keep itself running.

Two of them, the branchial hearts, push blood through the gills to load it with oxygen. The third, the systemic heart, sends it around the rest of the body.

And here's the strange part: when the octopus swims by jet propulsion, that main heart stops. Swimming, for an octopus, is holding its breath with the engine off. That's why, although it can shoot away when it must, it prefers to walk along the bottom on its eight arms: that's its power-saving mode.

It isn't its only extravagance: two thirds of its neurons aren't in its head but spread through its arms, which can touch, taste and decide on their own. Seen up close, an octopus isn't an animal with three hearts — it's a committee that has learned to move.