Any dog lover will tell you their canine friend picks up on their mood and emotions. Now scientists have worked out exactly what is going on inside a dog's brain when it sees a human - even a complete stranger - smiling or scowling. Their research involved 14 dogs in total who all sat very still in a brain scanner while they were shown pictures of people's faces. Photographs of happy, smiling human faces made an area of the brain that is associated with reward "light up" with activity. This reward circuitry is the part of the brain that is activated when we enjoy and remember good things, like tasty food or praise.