Are you serious? Relaxed-open mouth may unveil the competitive/cooperative nature of play fighting in kittens of two feline species

Play fighting is a multifunctional behaviour allowing the development of both cooperative and competitive skills. During play fighting, animals perform ‘competitive’ actions that are typical of the agonistic context and/or ‘cooperative’ actions to avoid escalation into aggression. Several structural features of play fighting (asymmetry, duration, variability and repetition) provide information on whether a session is more, or less, competitive. In many mammalian species, the relaxed open mouth (ROM) is a metasignal that communicates that the interaction is playful. In the Felidae family, play fighting has been poorly investigated and it is challenging to tell whether play fights are cooperative or competitive. Here, we explored whether the ROM could provide information about the cooperative/competitive nature of play fighting in felines. To do so, we videorecorded and analysed dyadic play-fighting interactions in kittens of domestic cats, Felis silvestris catus, and Asian leopard cats, Prionailurus bengalensis. For both species, we found that play-fighting sessions with ROM were more symmetric, lasted longer, were less variable and showed lower evenness and repetition than those without ROM. As a whole, our results suggest that in both species ROM may help manage unpredictable play-fighting sessions and therefore this signal can be used to increase cooperation during the playful interaction, thus prolonging it.