Dogs and humans use the same brain mechanism to process social information. Your dog really can tell when you or other dogs are happy or sad! How crazy is that? I think it is amazing. My dog seems to know when I am sad and I always wondered if she really knew or just sensed what that I was upset. Our dog is very sensitive to the tone in our voices. She will leave the room if we raise our voice even in a normal discussion and now I know why!!