In the depths of our seas lives a monster with nine brains, three hearts, eight tentacles and it's one of the smartest beings on the planet. If that's not enough, the octopus has a boneless body, two enormous eyes that take up a quarter of its weight, and its brain and intestines exist in a single pouch. It's also a carnivorous predator that can change shape and colour at will, walk on land and sea, and even cross through fire.