When the feathers or fur along an animals spine is raised as a form of intimidation or out of fear.
Hackles are the erectile plumage or hair in the neck area of some birds and mammals.
In mammals, the hackles are the hairs of the neck and back which become erect when the animal is fearful, as part of the fight-or-flight response, or to show dominance over subordinate animals. Raising the hackles causes the animal to appear larger, and acts as a visual warning to other animals. Raised hackles are used by grey wolves as a dominance behavior, by moose preparing to attack, and by cats and striped hyena which are fearful or threatened.
Angry cats with "blown out" tails should also be tagged.