Scientists -- and dog lovers -- have long known that dogs are remarkably good at reading human laughs, frowns, and tears. But the biology behind this ability has remained largely unexplored, until now. In a current study published in the Cell Press journal iScience, researchers from the University of Vienna peered inside the brains of dogs as they viewed images of various expressions. The brain scans revealed that dogs process human smiles in a unique way and, for the first time, provided evidence that dogs can distinguish between certain negative facial expressions.