Hissing is a sharp, sibilant sound produced by forcing air through a narrow opening, often associated with animals like cats and snakes. It serves as a warning signal, indicating fear, aggression, or discomfort. In humans, hissing can occur when someone expresses annoyance or disapproval. The sound is created by the vibration of vocal cords or by the movement of air through the mouth. Hissing can also be heard in various contexts, such as when steam escapes from a kettle or when a snake feels threatened. It is a universal sound that conveys strong emotions or reactions.