In my never-ending quest to decide between Other Minds and The Soul of an Octopus whenever one of them goes on sale, I found this pretty terrific piece by Amia Srinivasan for London Review of Books from a few years ago.
The question of what subjective experience might be like for an octopus is complicated by the odd relationship between its brain and its body. An octopus’s arms have more neurons than its brain, about ten thousand neurons per sucker; the arms can taste and smell, and exhibit short-term memory. Each arm acts with considerable independence from the brain; even a surgically detached arm can reach and grasp, avoid painful stimuli, and change colour. (In The Soul of an Octopus, Montgomery imagines an octopus testing human intelligence by seeing how many colour patterns our severed arms can produce in one second.) Yet an octopus’s brain can exert executive control, ‘pulling itself together’ when it needs to, for example when an octopus puts out only a single inquisitive arm to inspect a stranger.