I'm not aware of scratching a horse's withers or biting behind their ears being commonly used as specific methods of encouragement during horse training. Horse training typically relies on positive reinforcement, negative reinforcement, or other humane and ethical methods to communicate with the horse and encourage desired behaviors.
Positive reinforcement involves rewarding the horse with treats, verbal praise, or a gentle pat when they exhibit the desired behavior. Negative reinforcement might involve the release of pressure when the horse performs the desired behavior correctly, like releasing rein pressure when they turn in the desired direction.
It is essential to treat animals with kindness and respect during training. While some horses might enjoy being scratched in certain areas, and it can build trust and positive associations, it is crucial to be aware of the horse's individual preferences and comfort levels. Biting a horse behind the ears, even gently, is not an appropriate training technique and can be interpreted as aggressive behavior, causing fear and anxiety in the horse.
If you are interested in horse training, it's essential to work with an experienced and knowledgeable trainer who uses modern and ethical methods. There are many effective and humane approaches to training that promote a positive and healthy relationship between the horse and the trainer. Remember, safety, respect, and the horse's welfare should always be the top priorities.