This line in particular stuck out to me:
One horse chose to exercise on the treadmill on two out of three of his trials. While that one horse may have had some predilection for exercise, the overwhelming preference was for “absolutely no exercise.”
Of course, working on a treadmill is very different from running free. But this result does correlate with how horses behave in nature. Feral horses spend less than 1 percent of their time moving more quickly than a walk, and they pick up their pace in only one situation: when they are being chased.
Tristan says “I FREAKING TOLD YOU SO, CRAZY LADY. I will go willingly forward when there is a mountain lion in the ring with us, and NOT ONE SECOND BEFORE THEN.”