Or consider its intelligence: In experiments carried out with the Common octopuses, individuals are faced with five opaque doors, only one of which has a crab, which they love to eat, hidden behind it. Different symbols are visible on each door. After a few tries, the octopus accidentally chooses the correct symbol. In subsequent trials, the octopus quickly recognizes the symbol and opens the correct door, even when they are all moved around. If a crab is placed behind a door with a different symbol the octopus quickly learns the new symbol. In other experiments octopuses have shown ability to distinguish symbols about as well as a three- or four-year-old child.
Octopuses also play—there is no other word—with objects that are of no apparent use to them, such as little balls thrown into their tanks. These behaviors, and others, are unique among animals without back-bones, and more sophisticated than any displayed by fish as well as many reptiles and mammals.