Spooking horses - urban legend?

[7rider]

When I've encountered folks on horses on trails (in the woods, that is), I talk to them as I approach.
First, is the call out to any cyclists behin me: "Horses up."
Then, I slow down and ask the rider how the horse handles bikes, say "lovely day to be outside, isn't it?" - stuff like that. I let the rider tell me if their horse is okay around bikes, and respond appropriately. I had a friend who had a horse and her take was that the horse doesn't necessarily recognize this wheeled contraption with a funny hat as human. If a voice comes out of it that is more or less human, then that usually puts them at ease (in her experience anyway).
I've never seen horses on MUTs and rarely on the street. The Mall in Washington DC is an exception, but I'm usually not on my bike, and those police horses are selected for duty as being well tolerant of crazy humans and their pesky ways. Aside: I once saw a video of horses being prepped for duty for the Obama inauguration - they were walked through a barn of screaming, yelling volunteers, getting into the faces of the horses. The animals just quietly sauntered through like it was nothing. Pretty neat.