Ahloy-Dallaire, J., Espinosa, J., Mason, G. 2018. Play and optimal welfare: Does play indicate the presence of positive affective states? Behavioural Processes 156, 3-15.
Play is commonly used to assess affective states in both humans and non-human animals. Play appears to be most common when animals are well-fed and not under any direct threats to fitness. Could play and...