Heightened arousal or alertness — Dogs

The story behind the answer

Raised hackles are the hair along a dog’s neck and back standing up (piloerection), triggered by the sympathetic nervous system—think “adrenaline on.” This signals heightened arousal or alertness, not one specific emotion. A dog may raise hackles when excited, startled, intensely focused, fearful, or potentially defensive. It can also make the dog look larger, a common mammalian response to arousal.

Context matters: paired with loose body language and a waggy tail, hackles may reflect excitement or curiosity; with stiff posture, hard stare, and a closed mouth, they may signal fear or possible aggression. They’re not a friendly greeting by themselves, nor simply a reaction to cold. Memory tip: “Hackles = H for Heightened.” Always read hackles alongside other signals—ears, tail, face, and movement—to understand what the dog is feeling.