“…It also applies to other groups of animals and to any encounter that involves competition, including predatory encounters [31,40,41] and play fighting [42][43][44]. Playful fighting is distinguishable from serious fighting on a variety of criteria [45][46][47], but what unifies them is that, in both forms of fighting, the animals compete to gain access for some advantage, most often that advantage being to contact a particular body target [42,48,49].…”