Ok, I'll admit it. Moon has a few things that scare him. Bikes, foals, shiny rails, (teepees, which were a big problem for us on the high prairie cross country course,) the usual stuff, really.
My dad recorded a show for us about a group of riders in Africa that had an encounter with a lioness. Evidently the lioness was looking for a meal and watched them for a while before she sprang into action and actually started chasing one of the riders.
She was faster than the horse, and when she had caught up to it she lept onto its back. Somehow, (this seems impossible,) the horse and rider got away.
Now, I don't know about your horses, I can only speak for Moon, but I can assure you he wouldn't have reacted well to a lion chasing him.
In fact, I'm sure he would have been on edge just walking through the tall grass if there had been a bit of a breeze.
If I would've been in this same situation with Moon, I think he would have run for his life from the lioness. He'd of run away with or without me on his back!