Horses have been shown to have similar facial expressions as humans and chimps. Just like humans, horses use the same muscles to alter their facial expressions. I’ll spare you the offal horse puns and get straight down to the research.

The study, published in PLOS ONE, builds on previous research that has shown that facial expression is important for horses to communicate. Researchers from Sussex University developed The Equine Facial Action Coding System (EquiFACS) to identify and code facial movements in horses. The tool allows researchers to measure facial expressions by looking at the underlying muscle movement. They suggest this is the first methodology that documents all of the facial movements of a horse. EquiFACS has been adapted from the original FACS system used for humans.

Researchers analyzed video footage of horses exhibiting a wide range of behaviors, looking particularly at different facial movements. They then carried out an anatomic investigation of the facial muscles behind these movement. Researchers identified 17 discrete facial movements, known as “action units,” in horses. There are 27 action units in humans and 13 in chimps.

“Horses are predominantly visual animals, with eyesight that's better than domestic cats and dogs, yet their use of facial expressions has been largely overlooked. What surprised us was the rich repertoire of complex facial movements in horses, and how many of them are similar to humans” co-author researcher Jennifer Wathan, said in a statement.

“Despite the differences in face structure between horses and humans, we were able to identify some similar expressions in relation to movements of the lips and eyes,” she added.

As the findings make cross species comparisons, researchers suggest this helps enhance our understanding of the function of communication and how it evolved. Co-author Professor Karen McComb explained, in a statement, that the results of the study add to a growing body of evidence that “social factors have had a significant influence on the evolution of facial expression.”