Standing tall, arms spread, changing colors—them's fighting words for an octopus.

Until recently, scientists thought the ocean dwellers didn't communicate with one another much at all. Rather than sending signals with their skin color and texture, octopuses—mostly solitary, except during mating—were thought to camouflage themselves with it.

But new video evidence suggests at least one kind of octopus—the common Sydney octopus (Octopus tetricus)—sends cues to its rivals about whether it will flee or flight. (Also see "Social Octopus Species Shatters Beliefs About Ocean Dwellers.")

The common Sydney octopus, also known as the gloomy octopus, were thought to be very independent: When they do come together to mate, the female often eats the male afterward.

So the researchers were surprised that Sydney