Purring is one of the most iconic sounds in the animal kingdom. It is a unique vocal feature shared by small-breed cats such as the domestic cat, bobcats, cheetahs, lynx and pumas. Larger breeds of cats, such as lions and tigers, do not exhibit true purring behavior. What makes a purr unique from other vocal noises is that it is produced during the entire respiratory cycle (both inhaling and exhaling). Research into the cause and purpose of this mystical sound has continued for decades. Most recently it is thought that this sound originates from the internal laryngeal muscles in the throat, which help control the opening and closing of the glottis (the space between the vocal folds in the larynx). By oscillating the muscles in this area, the vocal cords separate causing a distinct sound as air moves across the surface.
Many behaviorists believe that the original function of purring was to enable a kitten to tell its mother “all is well”. This conversation often occurs during nursing and, since a kitten cannot meow (vocalization during exhaling) while nursing, purring became a universal signal of contentment between mother and kitten. Although it is tempting to believe that cats purr simply because they are happy, it is more plausible that purring represents a broader means of communication. Older cats purr when they play or approach other cats and even when they are distressed, afraid or sick.