Stacy Westfall discusses marking behavior as a fundamental aspect of horse training. She explains how this technique, often used in clicker training, can quickly reinforce desired behaviors, or can accidentally mark a mistake as well. Stacy explains the powerful tool horses use with each other of simply not reacting, and why it works so well in a feedback loop. Key points include: The introduction of orphan foals Lefty and Stormy to an adult horse, Gabby Gabby's subtle communication and non-reactive responses to the foals' behavior The significance of not overreacting to accidental touches or movements when working with horses Stacy emphasizes that a deep understanding of marking behavior and its implementation can greatly enhance training effectiveness and improve overall communication between humans and horses.