Last weekend, I went into the paddock to put a halter on Lily so I could lead her out. She was standing too close to the feeder for me to reach her head without stretching from where I was standing by her shoulder. Before I could raise my hand to touch her chest (the signal I give her when I want her to back) she took a step backward so she was in the correct position for me to halter her. I was taken aback: Lily is one of the brighter horses I’ve handled, but it seemed a bit much for her to realize that I couldn’t get to her head easily so she had to help me out.
Back in the early 20th century, Clever Hans was a horse that was purported to do arithmetic and other intellectual tasks. After an investigation, psychologist Oskar Pfungst demonstrated that the horse was actually reacting to the involuntary cues of his trainer, which were not perceptible by human observers. Even more interesting: Pfungst could not suppress the cues when he was handling the horse himself.
So I think what actually happened when I thought about asking Lily to back, I gave her a cue without realizing it, caught by her peripheral vision. Which is rather amazing in and of itself. But then there was a time when I had a hard time remembering the correct aids for the canter when I rode any horse but Hap. Hap didn’t need no stinking canter aids: I thought “canter,” and he cantered.