...In order to survive, animals preyed upon in nature have to be sensitive to emotional energy and the intention behind it. Horses, zebras and deer will often graze unconcerned as a lion who has recently eaten a big meal walks right through their pasture. Yet when an agile carnivore is on the prowl, the herd will scatter long before the cat can get close.
The experience of living with human beings has given domesticated horses even more sophisticated skills. I've seen even the gentlest of geldings become noticeable agitated when his handler wears a mask of confidence and well being to hide anxiety. It's as if the person appears out of focus to the equine awareness system. The body language of someone "putting on a happy face" is incongruent with the rise in blood pressure, muscle tension and emotional intensity transmitted unconsciously by an individual who is actually afraid, frustrated or angry. Mainstream trainers explain this phenomenon by saying "the horse can smell your fear",but it's more subtle and complicated than that. A secure, well-cared for animal will often relax the moment his owner simply acknowledges a hidden feeling---even if it's still there. Let me say it again: the emotion doesn't have to change in order for the horse to show at least some improvement. The handler just has to make it conscious and the animal that was agitated seconds before will sigh, lick his lips or show some other visible sign of release.
The observation that horses mirror the "feeling behind the facade" is one of the key principles of equine facilitated psychotherapy. Most people don't believe it until they see it (experience it)...