Purring Has More Than One Meaning
Many cat lovers assume felines purr only when they’re content. And while it’s certainly true that a cat basking in the sun, half on her back, might purr as an expression of contentment, she might also purr when she’s afraid or in pain, say, during labor or when she has experienced physical trauma. The low frequency of the vibrations inside her body can ease breathing and is even thought by some to help to heal injuries.
Cats can also embed a high-frequency sound in their purring if they want you to do something, like feed them, according to researchers at Britain’s University of Sussex. Humans tend to interpret the sound as the cry of a baby that needs tending, which evolution has designed to be difficult to ignore.
FYI, cats who roar can’t purr, and cats who purr can’t roar. There’s a bone inside the vocal cords that’s flexible in a roaring cat and hardened in a purring cat, and the way air interacts with that bone while a cat breathes makes all the difference.