Cats learn at an early age that their owners will respond to the vocal signals they make. They are rewarded with attention, affection and most importantly, food. There are individual and breed related differences in the vocal characteristics of cats, the Siamese being notorious for loud, at times piercing wails and meows made at night.
Why and how cats purr is a mystery. The sound originates in the vocal chords that open and close 20 to 30 times per second in response to electrical impulses originating in the brain. Exactly what triggers the impulses is not known, but there is a calming and sedating effect generated by this behavior. Kittens purr in response to attention from their mother and a mother cat may even purr during labour. Cats are even known to purr in the face of pain and aggression.
Sometimes a cat will drool excessively when it goes into a trance like state of purring and relaxing. Excessive salivating may be seen by itself in the absence of purring. Signals from the brain stimulate the salivary glands and strings of clear,thick saliva will hang from the lips creating an image that causes unnecessary concern from an owner.
Mysterious creatures, cats! No wonder there are so many superstitions and associations with the supernatural.