1. Play-fighting;Aldis,1975
2. The role of learning phenomena in the ontogeny of exploration and play;Baldwin,1977
3. Cooperation and competition during dyadic play in domestic dogs, Canis familiaris;Bauer;Anim. Behav.,2007
4. How and why animals negotiate and agree to play’, in Animal Play;Bekoff,1998
5. A critical reanalysis of the ontogeny of mammalian social and locomotor play: an ethological hornet’s nest;Bekoff,1981