A Capacity for Joy

Play, which seems to be both a sign and a source of joy, has been increasingly studied in recent years. Play is definitely important to animals because joy often expresses itself in play, which many animals may indulge in all their lives. Some animals may play with objects. And in other animals, object play may become social play. In addition, animals sometimes find playmates across the barrier of species. However, to what extent animals playing games recognize implicit rules is not clear.