Could Your Dog's Tongue Be Telling You Something?

A new study has found that dogs lick their mouths as an involuntary response to angry human faces, further suggesting that dogs have an understanding of the emotional expressions of people. While mouth-licking has been associated with a dog’s response to food or uncertainty, this new research shows that it could be used as a communication signal when presented with visual cues of anger.

Animal behavior researchers in the United Kingdom and Brazil analyzed 17 healthy adult dogs of various breeds that were shown 1 positive and 1 negative expression from the same individual, either human or canine of either sex. The images were shown in conjunction with a positive or negative sound from the same species and gender.

The findings, published in Behavioural Processes, revealed that dogs mouth-licked more frequently after seeing a negative facial expression than one with a positive demeanor. And the mouth-licking occurred more often in reaction to human faces than to dogs faces. Interestingly, the reaction was specific to visual cues; audio clips of angry human voices did not produce the same response. This indicates that mouth-licking may be a reaction to what dogs see and not just to any form of negative context.

"Humans are known to be very visual in both intra- and inter-specific interactions, and because the vision of dogs is much poorer than [that of] humans, we often tend to think of them using their other senses to make sense of the world. But these results indicate that dogs may be using the visual display of mouth-licking to facilitate dog-human communication in particular," said Daniel Mills, FRVCS, co-author of the study and a professor of veterinary behavioral medicine at the University of Lincoln in Lincoln, England.

This study backs existing research that dogs respond to emotional signals and supports some of the communication abilities of pets that many owners have long-believed to be true.