When your best friend catches you in a bad mood, does she try to console you, give you space to cool off or lick her own face in an uncontrollable slobber?
If your best friend is a dog, this third reaction may be familiar to you. Dogs lick their own mouths, noses and jowls all the time. Certain cuteness-obsessed Internet communities call it a “mlem”; some animal behavior researchers prefer to call it mouth-licking, and offer many possible explanations for the quirky canine behavior. Mouth-licking has been described as a stress-coping mechanism, a spontaneous display of arousal or a way to communicate desire to play with a certain toy or munch a certain treat.
But according to a new study by animal behavior researchers from the University of Sao Paulo, Brazil, mouth-licking may actually be one of a dog’s best tools for reading and responding to human faces — in particular, angry faces. [10 Things You Didn’t Know About Dogs]
In the study, the researchers exposed 17 healthy adult dogs to a series of audio and video cues representing both positive and negative emotions. On two screens, the test dogs were shown a combination of happy and angry human faces, and happy and angry dog faces — all with accompanying audio recordings. The researchers documented any instances of mouth-licking as each pupper watched the presentation. In the end, they found that only the images of angry human faces proved to be a reliable trigger for mouth-licking.