the kazilik pair landed together a short distance away , their scarlet hides vivid with markings of black-edged green , like leopard-spots , and licking at the air with their long black tongues ; so close that laurence could hear emanating from their bodies a low , faint rumbling something like the purr of a cat and the hiss of a kettle combined , and see even against the still-light sky the thin lines of steam which wisped upwards and away from the narrow spikes along the ridges of their back .