The following information has been obtained from Wikipedia. In no way do I claim ownership over this information, but I am placing it here for scientific and informational purposes.How felines purr
Despite being a universally recognized phenomenon, the exact mechanism by which the cat purrs has been frustratingly elusive for scientists. This is partly because the cat has no obvious anatomical feature unique to it that would be responsible.
One hypothesis, backed up by electromyographic studies, is that cats produce the purring noise by fast twitching of the muscles in their larynx, which rapidly dilate and constrict the glottis, thus causing vibrations in the air both during inhalation and exhalation. Combined with the steady inhalation and exhalation of air as the cat breathes, a purring noise is produced with strong harmonics.Why felines purr
Above all, the purr is probably the cat's way of communicating to others (cats and humans) that it is in the mood to be sociable. The purring sound is frequently made at the same time that other 'sociable' signals are made, e.g. erect tail, slightly closed "contented" eyes. People usually interpret the purring of a domestic cat as an expression of some type of positive feeling.
This information has been copied from Wikipedia, the exact source of said information can be found at this web address:http://en.wikipedia.org/wiki/Purr
So, if you read the above information from Wikipedia, you would have learned that a cat's purr is produced through the rapid twitching of muscles in the larynx as the cat inhales and exhales. You would have also read that you can tell if a cat is in a purring mood by the way it looks. Does it's tale stand up? Are it's eyes in a half closed drowsy state?
You can also tell if a cat is ready to purr by the way it acts around you. It may weave in and out of your legs, and lean close to you as it walks by.
Now, read on for the how to on making your cat purr.