I used to do this great exercise with students after they had begun riding on contact and needed to understand how to ask for a bend. I would hold one of the inexpensive very flexible school crops and ask the students how to bend it into a shallow C shape. We'd experiment with applying pressure at one or both ends and pressure in the middle and come to the conclusion that it worked best if you put pressure on the ends in one direction, and pressure in the middle in the opposite direction.
Then I'd explain to them that the stick represented the spine of the horse, that their inside hand was the pressure on the head of the stick, the outside leg well behind the girth was the pressure on the tail of the stick, and an active inside leg was the pressure on the middle, pushing the barrel of the horse outward.
Then I'd have a little fun, simulating a rider riding a circle on reins alone, with the haunches and body trailing outside the arc, or how forgetting the active inside leg would cause the horse to straighten its body and then fall in on the turn.
Visual aids - I gots mad skills!