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
    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
    Lip smack Purses and alternatively closes and opens lips
    Grimace Mouth closed, pulls lips backward exposing teeth
    Presentation Presents its hindquarters with tail up
    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