Table 2.

Behaviors analyzed during experiment 1 (snake task) and experiment 2 (human intruder task)

Behavior	Description
Mild aggression
Frown	Wrinkles or moves eyebrows up and down
Ears back	Flattens ears against head
Yawn	Opens mouth wide, baring upper teeth
High aggression
Head/body lunge	Thrusts head or body forward
Cage shake	Shakes cage
Mouth threat	Opens mouth slightly, exposing lower teeth
Defense
Freezing	Motionless for ≥3 s
Startle	Jerks suddenly
Eye/head aversion	Avoids eye contact, shifts gaze or whole head
Piloerection	Hair stands on end
Move away	Retreats from the stimulus
Submission
Lip smack	Purses and alternatively closes and opens lips
Grimace	Mouth closed, pulls lips backward exposing teeth
Presentation	Presents its hindquarters with tail up
Approach
Look at	Makes eye contact
Move toward	Shifts body forward, closer to stimulus
>Touch	Handles with hand or foot
Take/eat reward	Picks up or mouths the food reward
Other behaviors (not directed toward the stimulus)
Manual exploration	Handles any part of its surrounding
Oral exploration	Licks or mouths any part of its surrounding
Locomotor stereotypies	Activities, such as circling, hopping, repeated three or more times
Self-directed activities	Scratches, grooms, holds, etc. any part of its body
Look away	Looks away while engaged in behavior not directed toward stimulus
Teeth gnashing	Chewing motion without food in mouth
Miscellaneous	Engages in any peculiar activity not described above