Why do sand cats purr but lions roar? Researchers hypothesize that this difference between the two feline species may be partly due to a U-shaped bone in their throats called the hyoid. Sand cats, which are much smaller than lions, have a rigid hyoid that rumbles when the cat’s larynx vibrates, resulting in a purr. By contrast, lions have a somewhat flexible hyoid, and the bone is attached to the skull with a stretchy ligament that sand cats lack. These traits allow lions and most other species of big cats to produce powerful roars. The same traits may also prevent most big cats from purring.