The genus Panthera has long been treated as the roaring cats, but the snow leopard breaks the pattern. Its hyoid apparatus is incompletely ossified, matching lions and tigers, yet it produces no true roar. The difference sits in the larynx: the snow leopard lacks the thick, fat-and-elastin-rich vocal fold that lets a lion drive very low-frequency oscillations at modest airflow.
What it does produce is a long, low, pulsing call, and at close range the friendly chuffing sound, a non-threatening puff of air through the nostrils that is shared with tigers and jaguars. It also hisses, growls and mews.
The older textbook rule that the divide between roaring and purring cats is set by whether the hyoid is bony or ligamentous is the point most often got wrong. The snow leopard is the standing counterexample, and current accounts place the decisive difference in vocal-fold morphology rather than in the hyoid alone.