Almost every dog owner has found out that when they are really sad, their dog acts differently toward them. A dog may approach its disturbed owner with a concerned look and, quite out of character, hunker down next to them as if to provide some emotional support. It is as if they are saying, I know there is something wrong, I do not know what it is but I am here for you, anyway.
Are there other explanations? Of course, there are, but none make as much sense. You could argue that the dog observes your posture and appearance as submissive and, almost reflexively, approaches to investigate or respond to the new situation. Perhaps, seeing you in a submissive posture, the dog feels it has to grovel to remain below you in rank.
All dog owners like to think that their pet can sense their mood and emotions. Although researchers now accept that dogs, and other non-human animals, can experience primary emotions such as anxiety, fear, and anger, they still do not accept that "animals" have a sense of self and are capable of sophisticated secondary emotions. Instead, the scientists believe that non-human animals are incapable of understanding the feelings of others around them. Without a sense of self, they say, secondary emotions are impossible.
This is a complicated argument, and not everyone agrees with the scientists. I think animals should be given the benefit of the doubt. Let's assume that higher animals, like dogs, are sensitive creatures with feelings and emotions that can and do project beyond the blatantly obvious.
How about the time you came home to find your dog destroyed something? Did you find the guilty party hiding, or perhaps with a hangdog look? Many believe their dog is feeling guilty about what he has done. If you accept the guilt explanation, you must also accept that the dog is able to project about your feelings of disappointment or anger. Hard line behaviorists disagree with this interpretation, preferring to believe that the dog simply associates his owner, the damage, and his own presence with past punishment and acts submissively. But, what about the first time this happens? Maybe the dog "read" their owner's disappointment from their expression, because they sure were not responding to punishment.
Examples of dogs seemingly picking up on our emotions are endless but still the scientific proof is not there. I suppose it would be very difficult for some folks to accept that dogs, or any animals, might have minds that work in ways similar to our own. I suppose the believers still have a long way to go to convince the skeptics.
From an evolutionary point of view, it would be very strange if dogs did not have the ability to sense mood. It does not make sense to have a pack animal like a dog unequipped to realize when he was getting into trouble with another dog or when his behavior was having the desired effect. If dogs feel what we feel, they should be happy when we are happy, sad when we are sad, and hiding or hangdog when we are angry. All of the above does occur, on an almost daily basis, in our homes.