" an octopus may have half a billion nerve cells distributed between its brain and its “arms” (a mouse, by comparison, has only 75 to 100 million). There is a remarkable degree of organization in the octopus brain, with dozens of functionally distinct lobes in the brain and similarities to the learning and memory systems of mammals. Not only are cephalopods easily trained to discriminate test shapes and objects, but some can learn by observation, a power otherwise confined to certain birds and mammals. They have remarkable powers of camouflage and can signal complex emotions and intentions by changing their skin colors, patterns, and textures. "

― Oliver Sacks , The River of Consciousness