Cats hiss primarily as a defensive behavior to communicate fear, anxiety, stress, discomfort, or pain. It serves as a warning to others to back off and not come closer, signaling that the cat feels threatened or unsafe. Hissing can happen in various situations such as encountering unfamiliar people, animals, or objects, feeling overstimulated by petting, being scared, stressed due to changes in environment, or when they are in pain. It is essentially a way for cats to protect themselves by trying to appear intimidating and warning others before resorting to more aggressive behavior. Common reasons for cat hissing include anxiety or stress, fear of unknown threats, petting aggression when overstimulated, territorial defense, and discomfort or pain from injury or illness. When hissing, cats often accompany it with body language like flattened ears, arched backs, and exposed teeth to reinforce the warning. Understanding these signals helps in respecting their boundaries and reducing their stress.