Horses are extremely sensitive animals. They communicate primarily through body language. The following is one of my favourite quotes slightly modified to refer to horsemanship.
Horses are always reading your body language.
Your body language is your actions, your expression and your attitude.
Your thoughts become your attitude, your expression and your actions.
So in a way your horse can read your mind.
Of course horses don`t read minds. It just seems that way sometimes. Horses sense everything about you. They see the expression on your face, your posture, your attitude, the way you move, where you move. They sense immediately if you are tense or relaxed; if you are confident or insecure, if you are happy, worried or angry. They are aware of your focus and when you are in the saddle they can tell where your eyes are focused. They respond or react based on what they sense from you.
When you have the opportunity, watch someone else with their horse. Observe every detail of the human and the horse. If the human is relaxed and moves with rythmn and confidence the horse will respond in kind. Compare how a novice interacts with a horse to the interaction between an experienced horseman/clinician. When you are watching professionals in training videos do a few runs where you just watch the clinician and the horse and look at the behaviour and forget the purpose of the lesson . The lessons are important but you will get more if you are aware of all components of the horse human interaction.
If you have the opportunity video yourself interacting with the horse and do a very careful review of your behaviour. This can be a very humbling experience. What you think you are doing may look very different on screen. You have to swallow your pride and learn. Observe how the horse is behaving at every step. When you have trained your eye to look at details you will really begin to see the connections between horse and human. Do several sessions over time. Watch and rewatch , observe and compare, adjust and readjust, keeping working towards UNITY.
Any time you are with your horse look in your mental mirror. Do a check on how you are feeling, are you smiling or frowning, are you moving smoothly, is your body tense or relaxed, are your hands open or clenched, is your breathing regular, are you holding your breath, be aware of everything about yourself. Your horse uses all of these things in making up their minds about how they feel about you. (picture from pixdaus.com)
When working with horses attention to detail is essential. You must prepare your mind to recognize the slightest change in the mental, physical and emotional state of both the horse and yourself. You must prepare your body to respond to the horse, to have the feel, that is needed to make the correct adjustments to achieve the desired result. It is disciplined relaxation and finely tuned awareness of yourself and the horse. You will find that developing these senses of observation will translate from horsemanship to all aspects of life.