Ever noticed the fur on your dog’s back and neck suddenly standing up on end? This is called piloerection - more commonly known as raised hackles. People often assume when a dog’s hackles are raised it simply means aggression, but that’s not the whole story! Piloerection is an automatic response of the sympathetic nervous system, triggered by fear, stress, arousal or excitement. To understand what your dog is really feeling, you need to look at the whole picture, not just the raised hackles.