Arms Grow Back

Lose an arm to a predator and an octopus simply grows a new one. Within days a small bud appears at the wound, and over the following months it stretches into a full-length arm — complete with fresh suckers and its own nerve cord.

What makes this harder than it sounds is that an arm is not just muscle. The octopus has to rebuild the bundle of nerves that lets the arm taste, feel, and decide on its own. When it is done, the replacement works just as well as the original.

Through Any Gap

With no bones, an octopus can pour its whole body through an opening barely wider than a coin. Crabs hide in cracks; sunken jars and pipes make tidy dens. A shape that flows wherever it needs to go is a serious advantage.

There is one limit. The octopus's hard, parrot-like beak is the only rigid part of it, so any gap it tries to squeeze through has to be at least as wide as that beak. Everything else is soft enough to fold, stretch, and flatten out of the way.