About two-thirds of an octopus’s neurons are not in its head but in its arms, and the suckers along those arms can taste. Each one is lined with receptors that respond to the chemicals on whatever it touches, so an arm feeling its way into a crack in the rock, where the eyes can’t follow, already knows more or less whether it has found a crab or a stone. People who watch them hunt describe arms that seem to make up their own minds: one reaching, testing, letting go, while the rest of the animal is busy looking somewhere else. We talk about not being able to put a finger on something, as if fingers only point. For an octopus, touching a thing and finding out what it is are the same act, done eight times over, mostly without consulting the head.