Octopuses have three hearts. Two pump blood to the gills, and the third pumps it to the rest of the body.
Their blood is blue, colored by a copper-based protein called hemocyanin instead of iron-based hemoglobin.
An octopus has no bones at all, letting it squeeze its entire body through any gap larger than its beak.
Octopuses have nine brains: one central brain plus a mini-brain in each of their eight arms.
Hundreds of suckers line each arm, letting octopuses taste and smell whatever they touch.
They can change both color and skin texture in under a second to vanish into their surroundings.
The mimic octopus can impersonate other sea creatures, like lionfish and sea snakes, to scare off predators.
Octopuses are remarkably intelligent, using tools like coconut shells and rocks to build shelters.
Most octopuses live just one to two years, and females die shortly after their eggs hatch.