This photo shows a horse performing a movement called "shoulder fore" at liberty (loose, without being told to perform the movement). shoulder fore is a movement in which the horse is bent to the inside, leading with their outside shoulder, and stepping under themselves with their haunches. This is a moderately difficult dressage move, and less commonly used that simple leg yields or shoulder in. All dressage moves are controlled versions of movements horses perform regularly in play or herd behavior. Much of dressage training isn't teaching horses to perform certain moves, but teaching horse to balance in those movements with a rider, and understand complicated aids to perform unusual movements. (For example, in shoulder fore the horse is moving forward and sideways simultaneously. The horse's neck/spine, haunches, and shoulders are all doing slightly different things so to perform this movement undersaddle requires an education to understand the riders aids this clearly.)
