Your dog just gets you. He celebrates with you when you're happy; he curls up in your lap when you're sad. It's like he can read your mind. Nope, not your mind. Your face.
In you-already-knew-but-didn't-know-why news, your dog knows how to read your emotions as they play out across your face. He knows to look left.
Why left? Our highly specialized human facial muscles can subtly (or sometimes not so subtly) express hundreds of shades of emotion to allow others to judge our moods. In what is truly proof of their status as man's best friend, dogs have learned to recognize and capitalize on this human trait. When looking at a human face, dogs have what is called a left gaze bias. Looking left first and for longer (to the right, more emotional side of our faces) clues them in to our mood so they can adapt their behavior accordingly.
Check out this Telegraph article about a 2008 study at the University of Lincoln, UK. These scientists filmed dogs looking at various images — inanimate objects, monkeys, other dogs and humans — and charted their resulting eye and head movement. Turns out, they only looked to the left when presented with a human face.
It makes sense. As domesticated animals, dogs have evolved over hundreds of generations to be dependent on humans so no doubt their radar for human emotion has evolved as well. After all, understanding how a human is feeling helps a dog know if he's happy and therefore is safe to approach or angry and could pose a threat. It helps them connect emotionally with humans and therefore ensures that meals keep appearing on schedule.
Maybe that sounds like your dog is taking advantage of your emotions to ensure his own survival. In a way that's true. Biologically, every species has, through trial and error, determined some subconscious best practices and dogs are no different. But it's also proof that your emotional connection with your dog is not in your head. It's a loving, two-way street and that feels pretty good.