An owner reinforces the horse's yawn with a treat. What training concept does this illustrate?

The scenario where an owner reinforces a horse's yawn with a treat illustrates the concept of capturing. Capturing is a training technique where an animal's natural behavior is reinforced by providing a reward when that behavior occurs. By giving a treat when the horse yawns, the owner is effectively acknowledging and rewarding this spontaneous behavior, which can lead to an increase in the frequency of yawning over time.

This method differs from luring, which involves using a treat to guide the animal into a specific behavior, rather than waiting for the behavior to naturally occur. It also contrasts with targeting, where an animal is taught to touch a designated object or target. Classic conditioning focuses more on associating a neutral stimulus with a significant one to elicit a response, rather than rewarding a specific behavior in its natural context. Thus, capturing is the most accurate term for the practice described in the question.