When Nancy King got a pet octopus, she made a serious commitment: She wouldn't spend a night away from her home 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? But octopuses can be very interactive and show evidence of a surprising degree of intelligence.

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," King says.

Ollie was not unique in appearing to enjoy eliciting a response from humans. Denise Whatley 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.

"I've had several of them do this off and on for two hours," she says. "With one, I would go sit down, and I wore myself out running back and forth - it was almost like it was laughing at me."

Interacting with an octopus is seemingly 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.

"I had one little guy, I'd put my hand in the tank and he'd rub on my fingers to be petted," Whatley says. "But he would never do this for my husband, even though he's the one who feeds the animals."

The rewards of communing with this 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.

Feeding is complicated and expensive - you can't run out to the pet store for octopus chow. "There's no such thing," King says. "You go to Whole Foods and buy shrimp."

And that's the easy route - live food is superior both for nutrition and enrichment. "They profit from hunting a bit, and they do like it better," King says.