All Cats purr, some more or less than others. Scientific research reveals that all cats purr at the same frequency of 25 cycles per second. However, it is still a scientific mystery on what exactly causes the purring sound in cats. There are many theories as to what causes the sound of a cat's purr. Some believe that purring comes about through the cat's cardiovascular system, not the lungs or throat.
   Cats purr perhaps when they are in a state of enjoying or contentment. Newborn kittens purr as a sign of health and their mother uses purring to reassure her litter that all is well.