It was only the flickering light of the clouds that made their mitred double heads seem to move, but as Carter stumbled on he saw arise from their shadowy caps great forms whose motions were no delusion. Winged and whirring, those forms grew larger each moment, and the traveller knew his stumbling was at an end. They were not any birds or bats known elsewhere on earth or in dreamland, for they were larger than elephants and had heads like a horse's. Carter knew that they must be the Shantak-birds of ill rumour, and wondered no more what evil guardians and nameless sentinels made men avoid the boreal rock desert. And as he stopped in final resignation he dared at last to look behind him, where indeed was trotting the squat slant-eyed trader of evil legend, grinning astride a lean yak and leading on a noxious horde of leering Shantaks to whose wings still clung the rime and nitre of the nether pits.