TOOL USE

Octopuses will carry around two halves of an empty coconut shell and then hide inside them to avoid predators, a team of Australian researchers reported in late 2009. (Videos of this trick are easy to find on YouTube.) Tool use is considered a mark of cognitive sophistication; aside from humans, only a few creaturesincluding some primates, certain birds, and dolphinshave been shown to make and use tools. So far, the octopus is the only invertebrate known to manipulate tools..

PROBLEM SOLVING

It requires a certain kind of smarts for a creature to recognize that its efforts to solve a problem aren't working, and then to switch to a new strategy. The octopus seems capable of just that. Clams, which make up a major portion of the octopus diet, are difficult to open: Some have shells weak enough to just yank open, while others require the octopus to drill into the shell or chip around the edges. Mather and her colleague Roland Anderson, a biologist formerly at the Seattle Aquarium, decided to surprise octopuses by wiring shut clams that are usually easy to open. After trying in vain to yank the shells open, the animals quickly changed their approach, drilling into the clams instead. "The octopus is very good at trying different strategies," Mather said.

STEALTH MOTION CAMOUFLAGE

Hanlon calls it "the moving rock trick": When an octopus has to move across the open sea, it will take on the appearance of a rock and slowly creep along the ocean floor. "What's really sophisticated," Hanlon said, "is that they will adjust their speed based upon the amount of apparent motion in the water." More motion to distract from the octopus, and the creature will move more quickly. If the sea is calm and still, the cephalopod tiptoes more slowly. "It takes a big brain, excellent eyes, and magnificent coordination to pull off this cunning trick," Hanlon said.

SPATIAL MAPPING

In the wild, an octopus may go out foraging for hours, winding through numerous different types of habitats. And then, "suddenly," Hanlon said, "they'll leap up in the water column and make a beeline back home." In laboratory experiments, Hanlon and others have shown that the cephalopods can recognize environmental landmarks and use them to navigate. It sounds simple, but it requires some serious smartsthe creatures are essentially creating abstract mental maps of their environments and then storing and retrieving them from their long-term memories.

PLAY

Play, a behavior restricted to the most intelligent species, is a sign of an active mind at work, and there are some indications that an octopus can play. When Mather and Anderson placed an empty pill bottle in an octopus tank, they observed that several of the creatures would blow a jet of water at the bottle, pushing the container into the tank's water current, then wait for the current to bring the bottle back, and blow it away again. "It's the water equivalent of bouncing a ball," Mather said.