I will do everything in my power to convince the horse he has committed a grave error and is on the verge of dying. The other would be serious charging along the lines of what is described in this post. As I said, a significant number of horses threaten me while going through the bonder but the threats are half hearted and uncertain, more testing than anything. They make these threats without getting within retaliation range of me. Then there are those horses who are serious and perfectly willing to close in and duke it out.
Flight is a fear response.
An attack is an aggressive response. Determined aggression in horses is so serious it must not be tolerated. Being attacked by a horse is beyond your worse nightmare. Unless this horse can be dealt with quickly, at the very least this horse is destined for the killers, at the most it will kill. It may cause some ruffled feathers and cries of indignation but the alternative would be worse.