Study: Dogs Lick Their Mouths as Response to Angry Faces

An international team of scientists from Brazil and the United Kingdom has analyzed mouth-licking behavior of domestic dogs, and found that this behavior is not simply a response to food or uncertainty, but appears to be used as a signal to try to communicate with humans in response to visual cues of anger.

According to Albuquerque et al, dogs have a functional understanding of emotional expressions. Image credit: Djul.

Dr. Natalia Albuquerque from the University of Sao Paulo and co-authors presented dogs with pairs of facial expressions (one positive and one negative from the same individual) combined with an emotionally charged vocalization (positive or negative) or a control sound (neutral) and coded their mouth-licking behavior.

“We found an effect of the valence of the face image dogs were seeing on the onset of the mouth-licking, with higher frequencies of this behavior in response to the negative faces compared to images with positive valence,” the researchers said.

“However, neither the sound being played nor the interaction between image valence and sound affected the behavior.”

“We also found an effect of species with mouth-licking occurring more often towards human stimuli.”

“Mouth-licking was triggered by visual cues only,” Dr. Albuquerque said.

“There was also a species effect, with dogs mouth-licking more often when looking at humans than at other dogs.”

“Most importantly, the findings indicate that this behavior is linked to the animals’ perception of negative emotions.”

The authors believe that this behavioral trait may have been selected during domestication.

The findings, combined with previous evidence of the cognitive processing of emotional expressions, suggest that dogs may have a functional understanding of emotional information and greatly increase our understanding of their emotional world.

“Humans are known to be very visual in both intra and inter-specific interactions, and because the vision of dogs is much poorer than humans, we often tend to think of them using their other senses to make sense of the world,” said co-author Professor Daniel Mills, from the University of Lincoln.

“But these results indicate that dogs may be using the visual display of mouth-licking to facilitate dog-human communication in particular.”

The results are published online in the journal Behavioural Processes.

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Natalia Albuquerque et al. 2018. Mouth-licking by dogs as a response to emotional stimuli. Behavioural Processes 146: 42-45; doi: 10.1016/j.beproc.2017.11.006