Today’s Wonder of the Day was inspired by Pati from Virginia Beach, VA. Pati Wonders, “Why do cats purr?” Thanks for WONDERing with us, Pati!

A dog may be man's best friend, but loud barking can be quite unpleasant. On the other hand, there's an animal that's furry and cuddly and makes some of the most soothing sounds the ear can hear. What are we talking about? A purring cat, of course!

If you've ever spent much time with a feline friend, you know the tell-tale purring sound that's unique to cats. Somewhere between a low rumbling and an idling lawn mower engine, a cat's purr is a distinctive sound that's hard to miss.

But what does it mean? If you've ever seen a cat resting in the sunshine, you might assume that the purring you hear means the cat is happy and content. That may certainly be the case, as you might very well hear similar purring when you're snuggling with a cat and scratching it behind the ears.

Experts who have studied cats, however, will tell you that purring doesn't necessarily equate to happiness and contentment. Instead, studies have shown that purring can express a range of emotions and serve multiple purposes.

For example, some experts believe purring is a basic form of communication hat mother cats teach kittens when they're just a few days old. In addition to helping a mother cat and her kittens keep track of each other, purring may also be an early bonding mechanism.

Purring, especially when combined with a pleading cry or meow, can also be used to communicate hunger. Experts believe this combination of sounds may mimic the cries of human babies, leading to a more effective way of getting their owners' attention when they're hungry.

Studies have shown that cats also purr when they're nervous or in pain. If that seems strange to you, consider that purring when in pain might be a mechanism cats use to soothe themselves.

In fact, experts who have studied cats believe that purring might actually help cats recover more quickly from injuries. The low frequency of purrs causes vibrations within the body that have been shown to help heal bones and wounds, build muscle, reduce pain, repair tendons, decrease swelling, and make breathing easier.

While it may seem strange that purring could have so many meanings and purposes, some experts believe purring is similar to something that humans do often: smiling. If you think about it, you probably smile when you're happy and content, as well as when you're nervous and sometimes even when you feel pain. You might also flash that smile when you're hungry and you want your parents to fix you a snack!

Purring occurs in some species of big cats, too. For example, bobcats, cheetahs, lynxes, and pumas are all known to purr. Purring is different from meowing in that it occurs during the entire respiratory cycle (both inhaling and exhaling).

Although scientists still don't completely understand how cats purr, most experts today believe that a special, repetitive activity in the cat's brain (called a neural oscillator) triggers special voice box muscles to open and close the glottis, which is the space between the vocal cords. As the vocal cords separate repeatedly, the purring sound is created as the diaphragm muscles push air past the vocal cords.

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Tomorrow’s Wonder of the Day is full of cups, trophies, and rings!