Industrial Light and Magic has nothing on this

You'll swear this is a movie special effect, but it's amazingly real life. This common octopus not only can mimic the background color of just about anything against (or into) which it's hiding, but can control tiny muscles in its skin to recreate the texture of the plants and rocks it's mimicking. It can even match the sway of the currents. Cuttlefish and squid can do this too.

Roger Hanlon, a senior scientist with the Woods Hole Oceanographic Institution in Massachusetts, frightened this octopus on a dive 10 years ago. Scientists know that the skin of the octopus is filled with millions of special color cells called chromatophores that, when clenched, can produce a wide array of colors. mirror-like and reflectorized cells underneath the chromatophores expand the animal's ability to camouflage invisibly. As it relaxes its muscles, the color cells shrink and the animal blanches.

Hanlon says the octopus appears to establish its camouflage by sight, even though it's colorblind. How it assesses — and then processes — the various and sundry complex backgrounds into which it vanishes is a mystery. The ability, says Hanlon, requires a complex brain.

Here's a better explanation from National Public Radio's Talk of the Nation Science Friday, and more amazing examples.

Hanlon says much more needs to be known about how animals perceive camouflage — or more accurately, optical illusion — saying "other animals see it very differently." I'd suggest the opposite idea: If this octopus fooled a human diver, which is rarely among its usual predators, then I'm guessing the usual predators are fooled in the same way, by not being able to distinguish visually between the plant (or rock, or coral) and the prey.