An Octopus's Three Hearts and Blue Blood

Two of an octopus’s three hearts pump blood through the gills; the third, systemic heart, sends it around the body. Its blood contains the copper-based protein hemocyanin, which gives it a blue color. During jet propulsion, when an octopus expels water, the systemic heart can briefly stop; this movement is physiologically demanding, so octopuses usually travel along the seafloor using their arms.