FAQ #7: Why do cats purr?
Purring is most often thought of as a soft vibration coming from a happy, content cat. Some cats have a very loud purr, and sometimes they have a quiet purr that is difficult to hear. You’ll most likely hear a cat purring when they’re sitting in their favorite person’s lap, getting their head scratched, or in the middle of playing their favorite game.
However, you may also hear your cat purr when it’s sitting on an 
exam room table in a veterinary clinic, or when you are having work done around your house. Cats will purr when they are scared or stressed as a method to try to soothe and calm down.
How do cats purr?
A purr is a noise generated in the throat by the larynx, specifically involving the hyoid apparatus. In small cats and house cats, the hyoid is mostly ossified, meaning it’s bony. The hardness of the bone allows the vibration required to generate a purr. A purr is continuous throughout breathing, meaning it occurs during both inspiration and expiration.
Big cats, which include lions, tigers, jaguars, and leopards, have a hyoid apparatus that is softer and is composed of cartilage instead of bone. The difference in the hyoid is what determines whether a cat can roar or purr – they can’t do both! Although large in size, cheetahs, and mountain lions are not classified as big cats based on this anatomic difference. They purr and do not roar. Lions have the largest hyoid apparatus, which makes their roar the loudest of all the big cats. You can hear a lion’s roar up to 5 miles away!
Purring benefits people too!
We have known for years that people who own pets live longer, less stressful lives. Recently, however, research has shown that people who specifically own cats were found to have lower blood pressure and fewer heart attacks than even those who own dogs and other pets. Researchers guess that purring may be what makes the difference.
So, if you do not currently own a cat, it’s time to go to a local shelter or rescue and pick one up! Cats are good for your heart.
