Pet dogs are known to understand and empathize with humans thus, rendering them as "man's best friend." A new study found that there is another animal that may come close: horses.

Turns out, horses can read facial expressions and even distinguish if a person is happy, angry, or even stressed. This suggests that horses understand people more than previously believed.

"We have known for a long time that horses are a socially sophisticated species but this is the first time we have seen that they can distinguish between positive and negative human facial expressions," says co-study leader Amy Smith from the University of Sussex.

The study involved 28 horses from five stables across Sussex and Surrey. The researchers showed the animals photos of unfamiliar humans showing a variety of positive and negative facial expressions.

The authors then observed the reactions of the horses as the photos were shown. They were not able to see the photos being flashed so as to avoid influencing the horses.

Angry Faces Elicited Significant Impact

The reaction of the horses to angry faces was very distinct.

The horses used its left eye more when viewing the angry faces. This is because the processes in the right area of the brain, which is associated with threatening stimuli, manifests in the left eye.

The horses also exhibited increased heart rate and other stress-related behaviors.

"It gives us a real insight into how they are viewing the situation and shows clearly that they see it as negative," says co-study leader Karen McComb.

The observation goes to show that angry facial expressions do not go unnoticed for horses. In fact, it results in negative effects to behavior and function.

Horses may also view angry faces as warning signs that makes them anticipate bad human action such as rough handling.

Explaining Horses' Unique Facial Reading Ability

McComb says there are various potential explanations for their study results.

First, horses may have acquired this ability from its ancestors. The species may have adapted emotional cues reading from other horses through time and this enables them to apply that ability to human facial expressions in its co-evolution.

Second, horses may have learned this ability from experience.

McComb says emotional awareness is possibly very vital in highly social animals like horses. Her team is continuing their research to determine the association between the species' emotional skills and social behavior.

The study was published in the journal Biology Letters.

Photo: Gary Graves | Flickr