Look at the evasions this horse is exhibiting: tossing the head, going behind the bit, taking his head to the side, swishing and wringing of the tail, excessive foaming.

What does that tell us?

Is the contact too heavy?

Is the rider paying attention to the horse?

Is this a natural gait for the horse?

Is the horse trying to tell us something? Are we listening?

Also notice the horse's front legs and his winging.