Play is universal among mammals, widespread among birds, and documented in reptiles, fish, and even some invertebrates. It is metabolically expensive, occasionally dangerous, and apparently purposeless — yet natural selection has preserved it across hundreds of millions of years of evolution. Why? The question is the Academy's own foundational mystery. Karl Groos proposed in The Play of Animals (1898) that play is practice for adult behaviour: kittens stalk because they will hunt. Herbert Spencer argued play discharges surplus energy. Jean Piaget saw it as cognitive assimilation. Brian Sutton-Smith, in The Ambiguity of Play (1997), catalogued seven rhetorics of play and concluded that the field had no unified theory. Gordon Burghardt, in The Genesis of Animal Play (2005), offered five criteria for recognising play — it is spontaneous, voluntary, repeated, performed in a relaxed state, and modified from its "serious" form — but these describe the phenomenon without explaining it. Recent work by Sergio Pellis and Vivien Pellis on rough-and-tumble play in rats suggests that play rewires the prefrontal cortex, building the flexible social cognition that adult life requires. But this functional account still does not explain why play feels like play — why it carries its own intrinsic reward. The Origin of Play belongs in the Body School because play is, before it is anything else, a bodily act: animals play with their bodies, in their bodies, and the felt quality of play — its lightness, its absorption, its purposelessness — is irreducibly physical.