]]>Generally speaking, an analysis of animal behavior is not considered scientific unless the animal is assumed, at least tacitly, to be operating according to the same means/end calculations that one would apply to economic transactions.
...
Why do animals play? Well, why shouldn't they? The real question is: Why does the existence of action carried out for the sheer pleasure of acting, the exertion of powers for the sheer pleasure of exerting them, strike us as mysterious? What does it tell us about ourselves that we instinctively assume that it is?