There is a special look and expression, even a sound, dogs make when they feel their own rush of oxytocin inside and under the skin. I have witnessed this firsthand many times.
With my own older adopted dog, there are many memories of her contented noises and sometimes boisterous body language. I will always remember the day we both knew she was home, permanently home.
The face she made spoke all the words we needed to know that she was unpacking, and letting go of any lingering doubt, fear or worry about us. We knew that our love, compassion and trust had filled every corner of her being, and squeezed out the tiniest bit of residual uneasiness she may have carried.
She knew she was home. She knew we were her home. That meeting of hearts, rather than minds, is a feeling you never forget.