Dogs presented with images of either human or dog faces with different emotional states (happy/playful or angry/aggressive) paired with a single vocalization (voices or barks) from the same individual with either a positive or negative emotional state or brown noise. Dogs look longer at the face whose expression is congruent to the emotional state of the vocalization, for both other dogs and humans. This is an ability previously known only in humans. The behavior of a dog can not always be an indication of its friendliness. This is because when a dog wags its tail, most people interpret this as the dog expressing happiness and friendliness. Though indeed tail wagging can express these positive emotions, tail wagging is also an indication of fear, insecurity, challenging of dominance, establishing social relationships or a warning that the dog may bite.