If you cut off an octopus’s arm, the severed limb will still move about for at least an hour. That’s because each arm has its own control system—a network of around 400,000 neurons that can guide its movements without any command from the creature’s brain.

The hundreds of suckers along each arm can also behave independently. If a sucker touches an object, it will change its shape to form a tight seal, and contract its muscles to create a powerful suction. It grabs and sucks, by reflex.

This setup allows the octopus to control its astonishing appendages without overly taxing its brain. Your arm has a small number of joints and can bend in a limited number of ways. But