Octopuses have unusual blood that is copper based instead of iron based like ours, so the blood of these animals appears blue.  It is believed that this variation evolved as copper based blood is more efficient at transporting oxygen in extremely cold water with little oxygen present.

Octopuses have the ability to hide in plain sight and blend into their surroundings.  This is done by changing their skin colour using pigment cells, and also skin texture by the use of muscles.  These interesting eight armed animals are the most intelligent of all invertebrates, and are thought to have the intelligence of a dog.  Studies have shown that they learn new tasks easily on their own, and also learn by watching another octopus complete a task.