Emotional contagion. It’s the way emotions trigger similar emotions in people around them. It’s the reason that everyone around you suddenly gets grumpy when you come into work late and irritated. It’s also the reason that when one dog barks, every other dog in the vicinity barks wildly, too. I’m barking! He’s barking! We’re all barking! We have a tendency to mimic the facial expressions and emotional states of those around us. And it happens quickly. It’s been called instinctual. Humans do this along with other primates and dogs.