Why is it that dogs seem to be able to read our emotions? Whether we're happy or sad, our fury friends seem to be there, either wagging their tails or staring at us. Well, new research indicates that dogs can tell the difference between happy and angry human facial expressions. However, whether or not they understand the emotions behind these faces is still up for debate. Researchers from the University of Vienna designed an experiment where eleven dogs were trained to associate either a happy oran angry face with a food reward. During this stage, each dog was shown only the upper half or lower half of a person's face. In a later test, the scientists showed the dogs images, either of human faces they had not seen in their training, or of just half a human face. The dogs then had to, to the best of their ability, spot the difference. Surprisingly, the dogs are able to tell the difference between the happy and angry face more often than not, suggesting that they can associate positive and negative feelings with a smile or a frown. "Our study demonstrates that dogs can （distinguish） angry and happy expressions in humans. They can tel that these two expressions have different meanings, and they can do this not only for people they know well, but even for faces they have never seen before," Ludwig Huber, senior author and head of the group at the University of Veterinary Medicine Vienna's Messerli Research Institute, said in a press release. This study isn't the first to test whether dogs could tell human emotional expressions, but it is the first to provide evidence of what we have always suspected. Huber and his colleagues believe their findings can be useful to pet owners when giving punishment or reward,making sure not to let their faces give it away. But perhaps the message is to smile more, because you can't fool a dog.