An octopus does not steer eight arms like a puppeteer pulling eight strings.
Its central brain sends instructions, but a remarkable share of the animal’s nerve cells lies elsewhere: along the arms. In the common octopus, an anatomical estimate counts about 350 million neurons in the eight arm nerve cords together, compared with about 40 million in the central brain. Each arm is also packed with muscle and hundreds of suckers that can sense and move.
That arrangement helps an arm bend, reach, and explore with considerable local control, while the brain coordinates larger goals. Scientists are still working out exactly how those levels cooperate. So an octopus’s limbs are neither wholly independent little brains nor simple obedient tools; they are part of a distributed nervous system built for flexible movement.