Dogs can definitely pick up on our emotions I think... they can tell when we are mad, sad or happy. I know Mollie could tell when I was sad after my sister was killed... she wouldn't leave my side for 3 months. She may have not known "what" was wrong, but she definitely know "something" was wrong. I think they can sense the vibes we put off, whether we intend for them to or not. So yes, I think they know when we are sad. I also think they can help those feelings go from sad, to happy, just with their presence.