In wild cat species who can roar, the epihyal bone, which forms part of the voice box, is replaced by a ligament that can be stretched. The more the ligament stretches, the deeper the sound of the roar that is generated when air passes over the vocal cords. Studies found that big cats’ deep roar is made possible by their vocal folds being flat and square, and able to withstand much stretching and shearing. Only the tiger, lion, leopard and jaguar can roar.
In cats who are not able to roar, the bones of the voice box form a fixed structure. The vocal cords are divided and vibrate as the cat breathes in and out. This enables the cat to purr, but prevents her from roaring.