Well if your reins were taken away could you honestly control your horse?
I went for a ride and the thought came to me, my answer is no. I dropped my reins and tried using my legs and my seat, he listens for some of it or not at all, but as soon as I touch the rein to go in the direction I want he goes that way.
So hypethically if you were riding your horse and the reins dissapeared somehow, could you still steer?