How do you read a horse's emotional state during training?

Reading a horse's emotional state during training requires developing the habit of observing the whole horse simultaneously rather than focusing on any single indicator, because the horse's emotional state is communicated through the integrated pattern of multiple signals — ear position, eye quality, muscle tension, breathing, tail carriage, weight distribution, and the overall quality of the horse's attention and engagement — rather than through any single visible marker. The foundational skill is learning to distinguish between the relaxed, attentive, learning-capable state and the aroused, flight-oriented, survival-focused state, because training that is applied when the horse is in the latter state is not productive regardless of the technique used. A horse in a learning-capable state shows soft, mobile ears that move responsively to sounds and stimuli, a soft and blinking eye rather than a fixed and wide one, relaxed muscles through the jaw and topline, normal breathing, and a quality of general attention that is curious and engaged rather than fixed and watchful. A horse approaching its flight threshold shows the reversal of these qualities — ears locking forward and fixing on a perceived threat, eye widening and hardening, muscles tightening through the neck and topline, breathing becoming shallower or more rapid, and weight shifting toward flight preparation. Between these two extremes is a range of arousal states that require more nuanced reading — the horse that is alert but not alarmed, the horse that is mildly concerned but still trainable, the horse that is approaching its threshold but has not yet crossed it. Developing the ability to read these intermediate states and to calibrate training pressure accordingly is one of the primary skills that distinguishes natural horsemanship practitioners from those who work from a fixed pressure protocol regardless of the horse's moment-to-moment state.