As proof of their
intelligence several studies have been done to test their
problem solving and
learning ability.
One of their favorite foods is lobster. When presented with a lobster inside a glass bottle with a stopper, the test animals quickly figured out how to remove the stopper and get out the snack. When the lid was screwed on, most could figure out how to unscrew the lid.
When the screw-on lid gave some of the subjects problems, they were placed in an aquarium with a window looking at a neighbor who had figured it out. When the other octopus received a treat in a bottle, the first would stop trying to get at theirs, and jet over to watch their neighbor. Generally after watching once they would rush back to their own bottle, open it, and enjoy their treat.
They have also been known to become quite attached to their keepers, to the point where they wont eat if their normal keeper is gone for too long. In some cases, they have become depressed and starved to death when they have had only one keeper and that person retires or quits.