The blood running through their hearts is blue.
Blue blood is thanks to the copper-rich protein hemocyanin which provides the oxygen to the blood.

Octopi have three hearts.
One heart pumps the blood around their body. The other two pump the oxygen that has been created by taking water in through its mouth and passing it over its gills. These smart hearts allow them to live underwater.

Camouflaging into their environment is an easy task.
Their skin and eyes have cells known as chromatophores which sense light and the colour of their surroundings. The skin can sense the colour of the habitat and change its colour accordingly.
It gets better!
The muscles under their skin help it change their body to match the texture of the environment.

They have no bones.
An octopus is made up of muscles. They contract and release them to stay upright, to squeeze into rock crevices and scoot along the ocean floor.

All head and foot, no body.
Cephalopod meaning head-foot (in Greek) describes the animal family where their heads connect straight to their arms and feet. Other cephalopods are squid, nautilus and cuttlefish.