Dogs do it.
The findings contradict a decades-old belief that only mammals and birds like cats, dolphins, parrots and people play, says Seattle Aquarium biologist Roland C. Anderson in a paper accepted for publication later this year in the Journal of Comparative Psychology. Octopuses are considered the smartest of the invertebrate family, much brighter than their oyster, snail and clam cousins, Anderson says. In his study, he defines play as randomly repeating an activity that has no immediate benefit to the animal. Studying how octopuses play may help scientists understand their behavior and how they survive, says Jean Geary Boal of the University of Texas Marine Biomedical Institute. Anderson found that two of eight octopuses studied showed playful behavior by squirting streams of water though their breathing funnel at empty plastic bottles floating in their tanks, pushing them into a current of water and allowing them to float back before squirting them again.