An octopus has three hearts. Two pump blood through the gills to pick up oxygen. The third pumps that oxygenated blood to the rest of the body. When the animal swims, the third heart stops beating entirely — which is why octopuses prefer crawling. Swimming literally exhausts them because their organs stop getting fresh blood.
That blood is blue. Not metaphorically — literally, visibly blue. Human blood uses iron-based haemoglobin to carry oxygen, making it red. Octopus blood uses a copper-based protein called hemocyanin. Copper binds to oxygen and turns blue. When the blood loses its oxygen, it turns completely clear.
Hemocyanin is less efficient than haemoglobin under normal conditions, but in cold, low-oxygen deep water it works better. The three hearts compensate by pumping harder. A completely alien engineering solution to the same problem every animal faces: get oxygen to the cells.
The arms might be the strangest part. An octopus has roughly 500 million neurons, and about two-thirds — around 330 million — live not in the brain but in the arms. Each arm can act semi-independently: a severed arm will still reach for and grasp objects on its own.
Lining those arms are more than 1,600 suckers, each one able to taste. A 2020 study in Cell by Harvard biologist Nicholas Bellono found a new class of chemotactile receptors in the suckers — found in no other animal on Earth. A follow-up on the cover of Nature in 2023 confirmed the finding. The suckers are roughly 100 times more sensitive than a human tongue.
For comparison:
- Hearts: octopus 3, human 1
- Blood colour: octopus blue (copper), human red (iron)
- Neurons in limbs: octopus ~330 million, human ~0
- Sucker sensitivity: 100× more sensitive than a human tongue
- Can taste by touching: octopus yes, human no
Evolution did not make the octopus a smarter version of us. It built a completely different kind of intelligence — one that thinks with its arms, tastes with its skin, and runs on blue blood pumped by three hearts that occasionally just stop.
The next time someone calls an octopus an alien, remember: it was here first. The oldest octopus fossil is roughly 330 million years old. Humans: about 0.3 million. The "alien" has seniority by a factor of a thousand.