Which condition is not classified as a blemish in horses?

A blemish in horses typically refers to a physical imperfection or unsightly feature that does not necessarily affect the horse's function or soundness but can impact its market value or appearance.

Parrot mouth is an example of a conformational defect where the upper jaw is longer than the lower jaw, which can affect the horse's bite and ability to eat, thus classifying it as a blemish since it has more than just cosmetic implications. On the other hand, conditions like ringbone and windpuffs can also be seen as blemishes due to their appearance and potential impact on the horse's marketability, despite they can indicate some level of physical issue.

The Flehmen response, however, is a natural behavior exhibited by horses when they curl back their lips to better sample smells, often used to detect pheromones or other chemical signals. This behavior does not indicate any physical defect, nor does it impact the horse’s appearance in a significant or negative way. Instead, it is a normal and healthy behavior, distinguishing it from the other options that represent physical conditions of the horse. Therefore, it is classified as a normal function rather than a blemish.