Table 2.
Definitions of facial expressions, bodily actions, and associated valence with supporting literature
| Behavior | Definition | Valence |
|---|---|---|
| Facial Expressions | ||
| Full open-mouth face | An expression of continuously changing movements with cheeks and upper lips raised, lip corners pulled pack, and lower lip depressed while the jaw is lowered so the mouth is open. Bottom and top teeth visible. | Positive25,29 |
| Half open-mouth face | Identical to the full open-mouth face, but with only the bottom teeth visible. | Positive29 |
| Open-mouth bared-teeth | A rigid expression with cheeks and upper lips raised, lip corners pulled pack, and lower lip depressed while the jaw is lowered so the mouth is open. Bottom and top teeth visible. | Negative25,27,30 |
| Closed-mouth bared-teeth | Upper lip raised, lips corners pulled back, and lower lip depressed. Upper and lower teeth usually visible | Negative27,30 |
| Pout | Lips separated and funneled outwards. | Negative11,31,32 |
| No Expression | Absence of any coherent facial muscle activations recognized as an expression in previous literature. | Neutral32,33 |
| Bodily Actions | ||
| Play actions | Play wrestling, pirouetting, solitary play, and somersaulting (see Plooij, 1984)28 | Positive34,35 |
| Grooming actions | Picking through the fur of another individual. | Positive36 |
| Breastfeeding | Having mother’s nipple in mouth. Actual sucking movements may or may not be seen. | Positive37 |
| Nuzzling | Unsuccessfully attempting to access the mother’s nipple. | Negative11 |
| Aggressive actions | Tantrums, hitting, slapping, pulling hair outside of playing, and dominance displays (see Plooij, 1984).28 | Negative11,35 |
| Self-scratching | Moving the nails over the skin of some part of the own body while bending the fingers. | Negative31,38,39 |
| Avoidance actions | Avoiding approaching conspecifics, resisting physical contact of conspecifics, and defending objects from conspecifics (see Plooij, 1984).28 All behaviors must occur outside of play. | Negative40 |
| Other actions | All coded behaviors that were not included in the above were considered to be neutral. Common examples are locomotion, climbing, laying down, sitting, object manipulation, and traveling. | Neutral41,42 |