Octopuses are the geniuses of the invertebrate world. They can navigate mazes, unscrew jars, and escape into neighboring tanks to feed. And now it seems that octopuses are even smart enough to have fun. Roland Anderson, a marine biologist at the Seattle Aquarium, and Jennifer Mather, an animal behaviorist at the University of Lethbridge in Alberta, Canada, were surprised to find that octopuses play. Birds and mammals engage in all sorts of play: cats bat at string; birds appear to soar for the sheer joy of it. Invertebrates, however, were thought to lack the sophistication to play, or as a scientist might define it, "to engage in repetitive behavior unrelated to food gathering or reproduction." Anderson had heard colleagues casually mention that octopuses seemed to like floating thermometers. "I happened to have a bottle of Tylenol that I was about done with, so we filled it with water and glued it shut," he says. When he put the pill bottle into a tank with an octopus, the octopus first brought the bottle to its mouth, in case it might be food. Then it gently pushed the bottle away with a squirt of water, directing it toward a current that brought it back toward the octopus. When the bottle returned, the octopus squirted it away again. One of the eight octopuses tested played with the bottle for nearly half an hour. Anderson says that octopuses will squirt water at objects that annoy them, "but then they blow quite hard." If that doesn't work, he says, the octopus might attack the object. That the octopuses repeatedly directed gentle squirts at the bottle, says Anderson, "is an indication that this might be play behavior."