When does a cat's fur stand on end? - briefly
A cat's fur stands on end primarily when it feels threatened, frightened, or is trying to appear larger to intimidate a perceived threat.
When does a cat's fur stand on end? - in detail
A cat's fur stands on end, a phenomenon known as piloerection, primarily as a response to specific physiological and emotional triggers. This reaction is controlled by the autonomic nervous system, which causes tiny muscles at the base of each hair follicle, called arrector pili muscles, to contract. The most common reason for this behavior is fear or aggression. When a cat feels threatened or encounters a perceived danger, such as a larger animal or an unfamiliar environment, its fur stands erect to make the animal appear larger and more intimidating to potential threats. This is an evolutionary adaptation designed to deter predators and assert dominance in confrontational situations. Additionally, cats may exhibit piloerection during moments of extreme excitement or arousal, such as during play or when encountering another cat in a territorial dispute. Environmental factors, such as sudden changes in temperature, can also cause a cat's fur to stand on end as a reflex to regulate body heat. In rare cases, medical conditions affecting the nervous system or skin may lead to persistent piloerection, requiring veterinary attention. Overall, this behavior is a natural and instinctive response that serves multiple purposes, from self-defense to emotional expression.