Non-verbal communication between horse and rider is the foundation of dressage.
It is up to a rider to open and maintain good two-way communication channels between horse and rider.
This book describes in detail when and how riders can use their body as well as auxiliary aids (whip and spur) to clearly communicate with a horse as they ride and train it.
Good riders must learn to speak equine and not expect a horse to become a mind reader.
Horses are very sensitive to touch and can easily le.