the purrs are produced by the vibration of "false vocal cords", present in the larynx, they have a double sound, as they are emitted both during inspiration and exhalation.
The puppies feel the purr of the mother, who emits them while breastfeeding as a sign of tranquility, after a few weeks they are able to reproduce them to show satisfaction for a good feed.
Growing up, the emission of this particular sound remains and sometimes takes on opposite meanings: irregular purrs constitute a state of maximum well-being, when they are regularized they indicate the desire to stop an activity that was pleasant.
Uniform but vigorous purrs symbolize the desire for something pleasant, while very loud purrs indicate that the cat is in pain and seeks help.
complex speech language system
The cat has a complicated vocal language, in fact there are a hundred different sounds that this little animal can produce, compared to only forty of the dog.