Your dog carries your stress in its body for months. A 2019 study in Scientific Reports measured cortisol in the hair of 58 dogs and their owners over a full year and found that the two rose and fell together. When you are stressed, your dog is stressed. When you calm down, so does it. The synchrony was not driven by walks, weather, or the dog's own life events. It was driven by the owner. Dogs whose owners scored higher on personality measures of anxiety showed higher cortisol year-round. The dog's body was tracking the owner's emotional state over months, not moments. The bond between a human and a dog is not a one-way relationship where the human provides and the dog receives. The dog is absorbing the household's emotional weather and carrying it in its endocrine system. Your bad month is its bad month. This is what 15,000 years of co-evolution looks like. The dog did not just learn to read your face. It learned to sync its chemistry to yours, and the hair on its back is keeping a record of how you have been feeling since the last time it was groomed. The next time someone says "it's just a dog," the cortisol data says otherwise. The dog is a mirror with a heartbeat, and the reflection goes deeper than behaviour. pubmed.ncbi.nlm.nih.gov/3117…