On the other hand, its visual cells are not far away from the crystalline as in vertebrate's eyes, enabling him to better use light. The visual process resembles that of reptiles and insects: a photographic reproduction of the environment is not reproduced in the back of the eye. The light and color variations are noticed only when movement occurs.
The first strategy of defense that an octopus uses when attacked is camouflage. Color changes start at the eyes. The octopus has millions of special color cells all over his skin that allow him to match his surroundings. These cells, called chromatophores, are small, elastic pigment-filled sacs that expand and contract as needed to control the pigments inside. "Each chromatophore is surrounded by a ring of muscle fibers, all of which are under the rapid and coordinated control of the large optic lobes of the brain." (Norman, "The Master of Camouflage") The texture of the skin can also change to match a wide variety of backgrounds and look like a rock, coral, sand or seaweed. The change of color and texture is done in a fraction of a second. To the predator's eyes, it may seem like the octopus just disappears.
When camouflage is not enough to escape from a predator and there is no shelter available, the octopus uses a second strategy: he releases a cloud of ink. The ink has two essential functions: it hides the animal, which helps him to escape, and disorients his attacker by temporarily numbing his sense of smell. A moray will have a lot of difficulty trying to find its pray on a cloud of murky waters. When the water finally clears, and the moray regains his sense of smell, the octopus is already gone. .
The ink is used not only as defense but also as an attack mechanism. It is not rare to see an octopus attack a lobster, in despite of the fact that the lobster is well protected by its hard carapace and pincers.
