"The snaffle work shapes the neck so that it creates the connection with the back, which is the only means of influencing the entire horse, front, middle, and hindquarters, and of establishing balance. The work with the snaffle is furthermore supposed to make the horse flexible.
The work with the double bridle builds on the snaffle work. It collects the horse more highly, brings the body mass closer, temporarily even entirely, to the haunches, and it flexes the poll."