When Nancy King got a pet octopus, she made a serious commitment: She wouldn't spend a night away from her home in Dallas the entire time she had it.

"I had decided it would be an experiment in whether I could have a relationship with an octopus," she says. "I sat with her every day and spent time with her, and I got rewarded for that."

If the closest you've gotten to an octopus is sushi, you probably wonder: Rewarded how? In fact, octopuses can be very interactive, and show evidence of a surprising degree of intelligence, even what seems like mischief-making.

King's Ollie demonstrated an ability to manipulate both objects and people by inventing a game. It made use of a glass-cleaning tool with two pieces held together by a magnet, one inside the tank and one outside.

"She learned that if she pulled off the inside of the cleaning magnet, the outside would drop off and we would come running," says King.

Ollie was not unique in appearing to enjoy getting a reaction out of humans. Denise Whatley of Atlanta teaches her octopuses that if they come to one corner of the tank, they'll get attention, and if they go to another spot, she'll take her hand out of the tank.

Interacting with an octopus is a lot like communicating with an alien, since these animals are vastly different from humans: Whatley points out that octopuses have three hearts, a brain surrounding the esophagus, blue blood and no bones. Yet keepers say that individual octopuses have different personalities, and some say they can tell humans apart.

The rewards of communing with this alien intelligence come at a high price, though. This is an animal with specialized needs.

For starters, it requires a lot of space. Whatley says an octopus needs at least a 55-gallon aquarium, with a second large tank for a sump to hold the complicated filtration equipment needed for a saltwater aquarium. Another backup tank setup is a good idea in case there's an emergency, like the octopus inking its tank, which can clog its gills and kill it.

Finally, you'd better have a good lid, because the octopus is a master of escape. And with all that, all you can keep in the tank is one octopus, because they'll eat any tank-mates, including other octopuses.