Cats purr for various reasons including communication, self-soothing, and healing. Kittens purr early to let their mothers know where they are and to attract their attention for feeding. Adult cats often purr when they are happy, relaxed, seeking attention, or even when they are injured or stressed as a form of pain relief and healing. Purring is produced by the rapid, rhythmic dilation and constriction of the glottis in the cat's larynx, vibrating the vocal cords during breathing. Cats also use different types of purrs to convey different messages, such as soliciting food from humans with a more urgent purr.