Everyone knows cats purr when they’re happy, but only the experienced feline aficionado knows cats also purr when feeling frightened, threatened, hungry or injured. A trip to the vet or hurt companion can cause kitty to purr as much as relaxing with his cherish person or grooming a fellow feline, then, making it important to pay attention to context to determine why your cat is purring.
 
Purring begins in your cat’s brain where rhythmic, repetitive nervous system activity sends a message to the muscles in his larynx. This causes the larynx, or voice box, to twitch anywhere from 25 to 150 vibrations per second. When your cat inhales and exhales, this prompts his vocal cords to separate, producing the comforting sound and vibration we know as purring.  While vets are not entirely sure why cats purr, they generally agree it is a soothing exercise for felines. Some compare the behavior to our own smiles: People smile when they’re happy, but also when they feel nervous or want something. In the same way, then, a cat’s purr can be an anxious behavior or attempt at grabbing our attention as much as it can be a sign that all is well. If your cat is relaxed, with his eyes closed and tail still, he’s likely giving you a big grin. But if he purrs around mealtime, for example, the purr is more likely a grab for attention than a sign of satisfaction. The function of your cat’s contented vibrations could go even deeper, though, according to some scientists who have studied the behavior. The frequency of purring falls within the range that helps promote tissue regeneration, leading some to believe that the behavior could very well have healing properties. They theorize these vibrations are beneficial for bone growth, pain relief and wound healing, and possibly even for repairing muscles and reducing swelling, which may explain why cats have been found purring next to an injured companion. This is good news for pet owners, who can also benefit from the healing vibrations. Studies have found cats to be the best pets for relieving stress and lowering blood pressure — and purring might just play a role in that.
 
It’s worth noting that not all cats in the animal kingdom can purr. While domestic cats can create the soothing vibrations, their cousins who roar cannot purr because the structures surrounding roaring cats’ larynxes aren’t firm enough. While roaring species make these loud noises to protect their prides and territory, smaller cats are more likely to hunt alone, spending long periods resting in between chases. They mark their territories with scent glands, and reserve purring for time spent lying around, which may help stimulate bones so they don’t become weak during the rest.