[Narrator] Octopuses can unscrew jars,

throw rocks, and solve complex problems,

but most of their 500 million neurons

aren’t in their brains.

They’re spread across eight arms that can smell,

taste, feel, and act with surprising independence.

So, what’s it like when your arms have minds of their own?

Here’s what scientists know

about these nine-brained invertebrates.

According to a researcher

studying the octopus nervous system,

each arm contains something like its own spinal cord.

Bundles of nerves connect to every sucker,

allowing for incredibly precise sensing and movement.

Because sensory and motor nerves are intertwined,

an arm can react to what it feels

without checking in with the central brain.

As an octopus moves across the seafloor,

its arms often wander in different directions,

following smells and investigating

whatever catches their attention.

Researchers think the arms

make many of these choices locally,

and that even a severed arm can keep moving

and reacting to its surroundings.

Octopus arms may wander independently,

but they pull together when the situation demands it,

forming a parachute to trap prey

or a torpedo to escape danger.

Scientists still don’t know exactly how that switch works.

There appears to be some central control

during complex tasks,

though the brain may simply choose which arms to use

and let them handle the details.

The octopus’ unusual setup allows scientists

to also explore deeper questions

about consciousness and identity.

If an arm has a different perspective

from an animal as a whole,

then selfhood becomes somewhat blurred.

Can a single self have multiple minds?

The octopus offers a way

to investigate questions like these,

but scientists still don’t know,

and octopuses aren’t making the investigation easy.

In captivity, they’re notorious for escaping,

overflowing their enclosures,

and even short-circuiting laboratories

by squirting water at the lights.

Perhaps we will only understand them

when they deign to be understood.

They will have to, in some sense, take us by the hand.