Interesting piece from Jesper Juul on play with this note about Brian Sutton-Smith:
On two occasions I heard Brian Sutton-Smith claim that play provides a modicum of joy in our pain-filled lives. Although that wasn’t meant as a definition of play, it is interesting by reversing the order of events: we aren’t safe, and therefore we play. Rather, play is the animal deliberately pretending to be safe, while play lasts.
I find it fascinating and rather pleasing that such a universal and cross-species activity still defies definition.