Horses have clear facial expressions for disappointment and frustration.
Horses can't hide their emotions
A team at the University of Lincoln conducted a food-reward task on 30 horses that left the animals either disappointed or frustrated.
When feeling disappointed, horses tend to blink a lot, lift their nostrils, stick their tongue out and make chewing movements.
If the beasts were frustrated, they showed more of the whites of their eyes and rotated their ears backwards.
Dr. Claire Ricci-Bonot, lead author of the study, said: "It is easier to assess the physical health of a horse. It is, however, more difficult to do it for the mental health.
"A better recognition and understanding of horses' emotions thanks to their facial expressions can lead to an improvement in the management of these animals - that is to say to try to remove situations which can generate negative emotions in horses.
"From the point of view of the riders, to be able to interpret the horses' facial expressions, would enable to avoid a situation which can compromise the safety of the rider e.g. recognise that the horse if afraid or something."