Final answer:
The question pertains to the biology of horse behavior and physiology, notably their body language when nostrils are dilated and ears are positioned to the side, traits that can indicate excitement or stress.
Step-by-step explanation:
The question appears to be related to the behavior and physiology of horses, which falls under the subject of Biology. Specifically, the inquiry is focused on equine body language, as indicated by dilated nostrils and ears positioned to the side. These characteristics can suggest various emotional states or physiological responses such as excitement, stress, or attentive listening. In the context of the passages provided, where horses display a range of behaviors in response to their environment or human interaction, understanding equine body language is crucial for interpreting their actions and ensuring appropriate care and handling.
From the examples given, it is apparent that the writers are attentive to the subtle cues horses provide through their body language and physical responses. One passage describes a horse that is rearing, illustrating a horse in motion and indicating its vitality and the skill required to handle such a spirited animal. Another passage references a horse listening intently to its surroundings, demonstrated by its erect ears and rigid stance, indicative of alertness or possible concern.