Dogs get jealous just like humans and, apparently, they read facial expressions like we do, too. For the first time, researchers have found evidence that dogs can gauge our emotions based solely on facial expressions—a major find, as no previous study has "convincingly shown" that non-human species have that ability, the researchers write in their study, published in Current Biology. Earlier studies found dogs could identify a face they knew from one they didn't, but the latest research suggests they actually recognize emotions, Smithsonian reports. University of Vienna researchers began by training 11 pet dogs to distinguish "picture pairs" in which 15 people made happy and angry faces, cropped to show either the upper or lower portion of the face. The dogs—including border collies, mixed breeds, a fox terrier, golden retriever, and German shepherd, National Geographic reports—chose an option with their nose on a touch screen and were rewarded for correct answers.
One group saw only upper photos, the other only lower; some were rewarded for responding to happy faces, and the others to angry. They were then tested on both the other half of the faces used in training, as well as an image of the left half of the face, plus upper and lower images of new faces. They were correct "more often than would be expected by random chance in every case," a press release explains. However, "we found that dogs for which the happy faces were rewarded learned the discrimination more quickly than dogs for which the angry faces were rewarded," write the researchers, perhaps because the dogs had been conditioned to steer clear of angry-looking people. In future trials, the researchers would like to work with puppies, cats, pigs, hand-raised wolves, and dogs with less human contact to see if the ability is learned or congenital. (Humans may only have four facial expressions.)