Umwelt. J. von Uexküll used the term “Umwelt” (meaning subjective universe) to characterize the particular perceptual world of a species or even an individual. The subject’s Umwelt is divided into two parts, the Merkwelt and the Wirkwelt, both forming a coherent entity. Merkwelt (“perceptual world”) refers to everything a subject perceives. Wirkwelt (“active world”) refers to everything a subject does. To be perceived by a subject, objects have to possess a feature (Merkmal) that matches a subject’s receptor. The perceived stimulus is then processed in the Merkorgan (“sense organ”), for example, the brain, where a meaning is attributed to each stimulus. This meaning can change depending on the context or the subject’s internal state. Thus, a stimulus can have different meanings to the subject. We thus have to keep in mind that the horse’s perceptual world differs strikingly from that of humans (Leblanc 2013).