House cats can't roar. They can be plenty loud when they feel like it, but they can't actually roar. On the other hand, their cousin the lion can't purr.
All cats can either purr or roar, but according to Live Science, they can't do both. Lots of cats species can purr, including the bobcat, ocelot, lynx, cougar and cheetah.
A cat's lovely purr of contentment is created in the larynx as the cat breathes in and out. It is a quick twitching of the vocal folds inside the voice box. Both the purr and roar are created with the hyoid system at the base of the skull. In purring cats, there is a bone in the hyoid, while roaring cats have a long, elastic ligament.
Roaring cats have long, heavy, fatty layers of tissue that make up their vocal cords. So big cats create low, loud rumbles — loud enough to reach a human's pain threshold.
