A horse can lick and chew because they are comfortable, feeling good and calm. A horse can also lick and chew after extreme stress because it has ended, not because they are more calm from the work.
A horse can rhythmically swing their lifted tail when their back is relaxed and mind is calm. They can also swish and wring their tail when their back is tight and mind is agitated or worried.
A horse can lower their neck and head because they are relaxed and content. They can also lower their head when they are about to buck, or have submitted to aggressive training.
How can you tell the difference? Learning to read the whole picture is essential. Reading expression, hearing the sound of the footfalls (heavy or soft), listening to the breathing, feeling the quality of movement through the back, watching the series of facial expressions that lead to release. Without an understanding of these, it’s hard to know if your horse is benefitting from your work, or submitting.
To clarify – a horse benefits from work when they become more relaxed, confident, and balanced.