how do they do that?

how the heck do cats purr??
Answers:
Actually, no one knows why they purr, except, presumably, the cats themselves. In fact, no one really seems to know how they purr either. You might assume that it's some kind of vibration in the larynx, as one science columnist suggests.

However, others, such as biologist Kelleen Flanagan of the MAD Scientist Network, subscribe to the notion that the sound is created by the vibration of blood vessels.

---

I believe it is the vibration of the cat version of the voice box . I used to know this!

---

We cannot purr, so we are interested in how cats can do it. It turns out that domestic cats, some wild cats like pumas and mountain lions (in general, any big cat that cannot roar) and even raccoons are all able to purr. Humans happen to smile and laugh when they are happy, and dogs wag their tails. So it is not unusual for an animal to have a physical reaction to happiness. Cats show happiness by purring. They may also purr when startled or upset.

It turns out that cats have special wiring! The wiring travels from the brain to the muscles in the voice box, and this wiring is able to vibrate the muscles so that they act as a valve for air flowing past the voice box. The muscles work both during inhalation and exhalation, which creates the impression that cats can purr continuously. The air passes through the valve, which opens and closes rapidly to create the purring sound.

---

Hi there.one study determined that purring involves activation of nerves within the voice box. These nerve signals cause vibration of the vocal cords while the diaphragm serves as a pump, pushing air in and out of the vibrating cords, thus creating a musical hum. Some veterinarians believes that purring is initiated from within the central nervous system and is a voluntary act. In other words, cats purr only when they want to.

The other theory is that the sound comes more from vibrating blood vessels than in the voicebox itself.

---

Along with felling happy, I've heard that they purr when they are hurting. Take a sec to see if a cat is hurt when it purrs but dosen't seem to happy.

---

The purr comes from two membrane folds, called false vocal cords, that are situated in the larynx behind the actual vocal cords. Cats purr at 26 cycles per second, the same as an idling diesel engine. Kitty purrs both when she inhales and exhales, all the time keeping her mouth completely closed. Scientists think purring is produced by blood in a large vein in the chest cavity that vibrates and is then magnified by air in the windpipe.