On Thursday morning, workers filing into the Santa Monica Pier Aquarium in California were surprised to find 200 gallons (750 liters) of seawater soaking into their spanking new, ecologically sensitive flooring. It turns out that a curious two-spotted octopus had disassembled a water recycling valve and directed a tube to spew out of the tank for about 10 hours, according to the Los Angeles Times.

"It found something loose and just pulled on it," the aquarium's education manager Tara Treiber told the Times. "They are very smart creatures."

Octopuses, some 300 species of which inhabit tropical waters around the world, can change colors, squirt out poison, and exert a force greater than their own body weight. But calling the eight-armed cousin of your garden snail "smart" seems a bit of a stretch. In fact, the animals are part of an elite group of slimy mollusks known as cephalopods that range from giant squid to the shelled nautilus and all have remarkably large "brains"—at least for creatures sans backbones.
Scientists have found that octopuses can navigate their way through mazes, solve problems quickly and remember those solutions, at least for the short term.

To find out more about octopus intelligence, we spoke to Jennifer Mather, a comparative psychologist at the University of Lethbridge in Alberta, Canada. Mather has been studying octopuses for 35 years in an effort to gain insight into the evolution of intelligence. While most scientists hold octopuses in high regard, it's worth noting that not everyone shares Mather's lofty assessment of their intellectual abilities and personalities.

[An edited transcript of the interview follows.]

Are octopuses smart?

Yes, but of course one has to ask what that means. I would say intelligence means learning information and using the information that you've learned.

So, how do you know they are smart?
We observed how octopuses figure out how to open clams and what sort of flexibility and variety they have. We give them clams and mussels in order to figure out which they like best. They are very strong, but we found they prefer mussels because mussels are easier to open. They switched to clams when we put the clams on a half shell. They clearly made a decision to go with what was easiest. We noticed along the way that yanking them open wasn't the only thing the octopuses could do to open them. They have a cartilaginous beak, which looks a lot like a parrot's beak, and they could chip at the edge of the clamshell and then they could inject poison and weaken the clam. Or they actually have a salivary papilla, and they can drill a hole to inject the toxin that way in the stronger clams. They were selective about what technique they would use with what species. We decided we would cheat on them: We took one of the easier ones and wired them shut. They switched techniques according to what would work best. Of course, this doesn't sound hard to you because you're a human, but most simple animals keep trying the same technique.

What other indications are there that octopuses are intelligent?
Octopuses play, and play is something that intelligent animals do. At the Seattle Aquarium, my colleague Roland Anderson and I figured out a situation in which they might play: a boring situation. We gave them an empty tank and a floating pill bottle and waited to see what would happen. Nothing happened the first time, but, after the fourth time, a couple animals did something we call "play." The octopus blew a jet of water at the pill bottle and that caused it to go over a water jet in the tank and come back to the octopus. These two individual animals did it in a sequence over 20 times. That's just exactly the kind of thing we do when we bounce a ball. When you bounce a ball, you are not trying to get rid of the ball, you are trying to figure out what you can do with the ball.

Octopuses also have personalities. We used the same kind of setup people use when they want to study human personalities. You just ask what do the animals commonly encounter during the day in different situations and look at the variability. We put them in three common situations: alerting (opening the top of the tank), threatening (touching the octopus with a test tube brush) and feeding (the octopus was given a crab to munch). This takes awhile because we tested 33 animals, each for two weeks. We found there are three dimensions and we settled for names: activity, reactivity and avoidance. Avoidance is how shy you are. Activity is if you are very active or passive. And reactivity indicates whether you are very emotional or more blasé. Octopuses can have any mix of those traits. We didn't take it any further, but there's a former graduate student in Australia looking at the extent to which personality affects ecology.

Do octopuses have brains?
The molluscan nervous system has a bunch of paired ganglia (a cluster of nerve cells), which in an animal like a clam or a snail are not very big and are widely distributed through the body. They control different functions and are located in different areas. Well, the cephalopods—that's the octopuses, squids and cuttlefish—they are unique in that all these ganglias have condensed so they form a centralized brain. The other thing that is unique amongst the mollusks is there are two areas of this brain that have developed that are specialized for memory storage. It's not just that the brain is larger and condensed, but they have areas of the brain dedicated to learning. That's the kind of thing we humans have, but it’s a completely different brain.

By invertebrate standards it’s a huge brain, but by vertebrate standards, it’s a small brain. What's interesting about the octopus is about one third of the neurons (nerve cells) are in the brain. They have a huge neural representation in the arms, and there's a ganglion controlling every sucker, so there's quite a bit of local control. As humans, we're very proud of having a pincer grasp—the thumb and forefinger—and we say that's responsible for our ability to manipulate the environment so well. The octopus can fold the two sides of its sucker together to form a pincer grasp and it can do that with every single one. It has a hundred pincer grasps.

Why do you think octopuses evolved such big brains?
Probably because the tropical coral reef is the most complex environment in the world. There's such a huge variety of situations, lots of kinds of prey, lots of predators, and if you are not armored, you'd better be smart. The octopus has gone the smart route. Also, we talk about mammalian intelligence evolving in social situations, but clearly the octopus, a solitary organism, has evolved intelligence to solve ecological problems.

Do octopuses often cause trouble in aquariums?
They are very strong, and it is practically impossible to keep an octopus in a tank unless you are very lucky. One of the early researchers said if you leave a floating thermometer in a tank, it will last about five minutes. Octopuses simply take things apart. I recall reading about someone who had built a robot submarine to putter around in a large aquarium tank. The octopus got a hold of it and took it apart piece by piece. There's a famous story from the Brighton Aquarium in England 100 years ago that an octopus there got out of its tank at night when no one was watching, went to the tank next door and ate one of the lumpfish and went back to his own tank and was sitting there the next morning. The aquarium lost several lumpfish before they figured out who was responsible.