Giant Pacific Octopus
When I was a kid, my father used to raise octopi in our basement in NYC as a hobby.  He had about six 55-gallon tanks arranged in two rows.<p>Every day, he'd come home from work, throw his hat and tie on the coatrack, and immediately head to the basement to play with them.  If you didn't play with them, they'd die of boredom, he said.<p>Their favorite game was "jar."  He's put empty Gerber and Ball jars in the tanks, with lids, and they'd swim in and out and in and out of the open jars.  Eventually, they'd learn to open the closed jars.  And then they'd spend hours swimming inside the jars, and closing the lids behind them, and trying different sized lids to see which ones worked on which jars.  It was all very fulfilling to my father.<p>I don't know what happened to the octopi when they got mature.  My guess is that he sold them to pet stores or restaurants or something.