Piloerection is the hair raised on the neck or along the spine on a Dog and is exact same involuntary behavior as in a human.
Being honest, I just wanted to use the word piloerection in a sentence to see if I could grab your attention. I will talk about it because it is something we look for when looking for signs to predict negative behavior.
OK, backing up here to explain the nature of this piece: Signs of Less Stress. There are plenty of discussions about observing the ears, eyes, mouth, posture, and movement to define the emotional state.
There SHOULD be more discussions on the nature of what is happening IN that animal = namely, the involuntary contractions of muscles controlled OR MORE ACCURATELY STATED: UNCONTROLLED by the sympathetic nervous system. Oh, don't get me going about the PARASYMPATHETIC NERVOUS SYSTEM - we'd be late for supper!
As my girlfriend in the photo displays - she has no control when looking at her ex-boyfriend or ex-co-worker walking into a room. She cannot help herself any more than the Dog sharing the picture with her has control wherein both are exposing their canine teeth, FYI = on the side facing the person of concern... according to Charles Darwin.
What I am trying to say is that these unscripted physical responses are as close as we will get to the truth of their thoughts, feelings and emotional states and therefore should NEVER BE PUNISHED, SCOLDED, SHAMED, RE-SHAPED, OR IGNORED. (Look at my un-Valentine's day story of The Great Dane's Growl and his warnings that were scolded then ignored until it was almost too late. True story.)
These expressions are as genuine as it gets! So says Charles Darwin in his book: “The Expression of the Emotions in Man and Animals,” first published in 1872, and long regarded as a seminal work in psychology. Here, Darwin makes the case for the instinctual or inherited nature of the facial expressions and body language that accompany our simple or primary emotions = anger and fear, surprise and disgust, joy and sadness, and other more complex emotions, too. Darwin terms these facial expressions and body language “the language of the emotions,” and deems them a product of natural selection, a process of evolution.
Getting back to piloerection in a dog and raising the hair on the back of our (human) necks, the cause is the same: involuntary contraction of muscles at the base of hair follicles. BTW, you're invited down any of these Rabbit holes I go down to find this fascinating yet ego-deflating information for the anthropocentric** thinker.
** Anthropocentric: #1: considering human beings as the most significant entity of the universe. #2: interpreting or regarding the world in terms of human values and experiences.