this is legit the reason people are not allowed to perform experiments on octopi, and any sort of surgery that has to be done on one in captivity for health reasons must be done with something to help lessen pain.
I think this all the time. Try going in pitch black with a picher of water, a flashlight, and a bowl. As you pour the water in to the bowl shine the flashlight across the water. It will move sightly with the light.