 Why was there fear for the wind shifting around the Hairy People?
Rolf swung the lax controls over hard as the bursts of fire revealed a looming barrier of stone dead ahead, and then he felt the tough skin of the flyer crumple inward. The floors of the thirty-seven caves through which they had so carefully jetted were a splintered, creviced series of canyon-like wastes, and as he ascended the rarefied atmosphere of the higher levels would spell death. Here at least the air was thick enough to support life, and somewhere nearby the outlaws who smuggled their precious contraband water into the water-starved domes of North Mars lay hidden. Toward this barrier the spinner bore him, and Rolf was content to let it move in that direction—from the heights of the wall he could scout out the country beyond. The spinner had slowed its speed; it seemed to Rolf that he must be falling free in space for a time, but the feeble gravity of the tiny world tugged at him more strongly as he neared the wall. And the barrier became a jumbled mass of roughly-dressed stone slabs, from whose earth-filled crevices sprouted green life. So slowly was the spinner dropping that the blackened desolation of the other hemisphere came sliding up beneath his boots. He drifted slowly toward the opposite loom of the mysterious wall with a swift wind off the desert behind him. Ten steps he took before an excited voice called out shrilly from the rocks ahead. This mysterious world that floated above the cavern floor might be their headquarters. "You know their leader, Cannon, wanted you.
 The wind would spread the scent of the Earthmen and cause an attack
 They wind would block the mind reading abilties of the Hairy People.  The wind would cause explosions.  The wind would spread the hair from the Hairy People and block vision.  The wind would spread the scent of the Earthmen and cause an attack