Two of the hearts work exclusively to move blood beyond the animal’s gills, while the third keeps circulation flowing for the organs. When the octopus swims, the organ heart stops beating, which explains why these creatures prefer to crawl rather than swim (it exhausts them).
An octopus also has nine brains — well, sort of. There’s one ‘main’ brain where all the analysis and decision making takes place and eight ancillary brains — one at the base of each arm — that function as preprocessors for all the information obtained by that arm. Two-thirds of an octopus’ neurons reside in its arms, which can independently figure out how to open a shellfish, for instance, while the main brain is busy doing something else.
Our blood is red due to the fact that it contains iron-based hemoglobin to transport oxygen to cells. Octopuses, on the other hand, use the copper-based cyanoglobin, which performs the same function, albeit less efficiently — this makes octopuses have less stamina than you might expect.