Science & TechFact
An octopus has three hearts and blue blood.
Two hearts push blood through the gills; the third supplies the body. That body heart stops while the animal swims, which is why octopuses prefer to crawl. Their blood is blue because it carries oxygen with copper-based hemocyanin instead of the iron-based hemoglobin in yours.
Useful: Copper binds oxygen better than iron in cold, oxygen-poor water: a deep-sea advantage.
Source: en.wikipedia.org