Which horse would you NOT purchase due to a major unsoundness affecting its usefulness?

A horse with a parrot mouth significantly impacts its usefulness because this dental deformity can affect the horse's ability to properly chew and digest food. The parrot mouth condition, also known as an overbite, can lead to various issues, including difficulty in eating, discomfort, and long-term health problems related to nutrition. This dental issue may hinder the horse's performance and overall well-being, making it a poor choice for purchase compared to the other options.

In contrast, a normal horse with high energy indicates good health and potential for performance. A horse with minimal past injuries suggests that it may have recovered sufficiently to maintain its usefulness. A horse with a clean bill of health presents no evident physical issues that would jeopardize its performance or usability. All of these options offer greater assurance regarding the horse's soundness compared to a horse with a parrot mouth.