Dogs have an astonishingly high level of emotional intelligence, but a new study suggests this might even be more than what we think.

Specifically, a new study from the University of São Paulo has concluded that dogs can very accurately read angry or negative emotions from humans, and reliably respond to it with, of all things, mouth-licking.

Famous within the Internet community, this action (lovingly called a “mlem”) has been seen as a cute and normal reaction.

Scientists have long theorized that this mlem is the dog’s reaction to stressors around him, while there are those who suggest that this is how a dog communicates his intent to munch on something or to play with his human.

Recently, this behavior has been linked to a dog’s ability to read human faces.


In the study, the researchers subjected 17 adult dogs to an experiment where they were shown various audio and video cues. These cues included both happy and angry expressions and spanned both human and canine examples.

There were pictures and audio recordings to accompany them. During this time, the researchers noted how many times the mouth-licking reaction was seen, and on which cues.

The result is somewhat surprising. The dogs reacted with the mlem only to images of angry human faces, and they were not triggered by audio cues as well. The reactions were also “species specific”, meaning they only reacted when they see the negative expression on human faces, and not when they look at dog faces.

The team, led by Natalia Albuquerque, found that angry human faces elicited about twice as much mouth-licking as the other visual cues. There was mouth-licking behavior noted in happy human faces as well, but the angry ones were the only reliable triggers.

Natalia and her team had published the study in the Behavioral Processes Journal.

Evolutionary Insights

These findings have led to theories that dogs and humans may have shared a significant portion of their behavioral evolution together.

The researchers themselves believe that the mlem was a behavior that first appeared when humans were still in the process of domesticating dogs. Mouth-licking became a way to better communicate with humans, especially since humans relied largely on visual cues for their communication.

The authors of the study also mentioned that the success of the canine as a species may have also hinged in their ability to recognize positive and negative expressions. This became especially important for dogs who had already been domesticated.

This body of knowledge is the freshest addition to the literature on canine emotional intelligence. Back in 2016, a study found that dogs can match human facial expressions with corresponding speech patterns. This is the very same team that Natalia, now a candidate for a doctorate in experimental psychology, now heads.

This means that the next time you see a cute-looking mlem, you should think twice about how you look to the dog in question. He may be acting quirky, but he may be closely reading your facial expressions and your actions.


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