Play(unrewarded and rewarded)

play can be both rewarded and unrewarded, unrewarded is just simple play for the fun with no later benifit, while rewarded is play that could have some kind of reward, such as strengthening pack/ speicies relations or possibly acting as a form of practice. I think this would only be available once a creature is of a certain intellegence, but would provide benifits like better pack orginization, pave the way to complex tool use, or something else. What do you think? how might this be implemented?