Figure 1: Rodent facial expressions.

(a) Pain grimace in rats: Orbital tightening, cheek flattening, folded, curled ears angled forwards or outwards (Sotocina et al., 2011) (b) Altered facial expression after tickling: Ear blushing and ears angled backwards (Finlayson et al., 2016) (c) In a mouse resident-intruder paradigm, the resident and intruder mice display two different facial expressions maintained during fighting: The resident displays tightened eyes and flattened ears, while the intruder displays widened eyes and erect ears (Defensor et al., 2012) (d) Examples of distinguishable facial expressions in mice: expressions after drinking sweet and bitter liquid, pain and freezing behavior (Dolensek et al., 2020) (e) In rats, whiskers are more protracted in social facial interactions before an aggressive interaction than in social facial interactions before nonaggressive interactions. (Wolfe et al., 2011). Figure permissions pending. Permissions: (a) Reproduced from (Sotocina et al., 2011) under a CC BY 2.0 license, (b) reproduced from (Finlayson et al., 2016) under a CC BY 4.0 license, (c) reproduced from (Defensor et al., 2012) with permission from Elsevier (d) reproduced from (Dolensek et al., 2020) with permission from AAAS (e) reproduced from (Wolfe et al., 2011) with permission from APA.