 Why would the Furry Ones not follow Rolf and the others when the retreated?
"Trapped us neatly," Rolf said through clenched teeth. 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. Without water and food certain death grinned in his face, for beyond the sand-buried entrance to these lost equatorial caves there were no pressure domes for hundreds of miles. How many hours later it was when the first faint glow of white light reached his eyes Rolf did not know—it had seemed an eternity of endless plodding along that smooth-floored descending tunnel. "They may have found the sunken seas of Mars," thought Rolf as he moved alertly forward, "water that would give the mining domes new life." 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. Deftly Rolf nested the spinners again in their pack before he set out toward the heaped-up mass of stone blocks that was the wall. Ten steps he took before an excited voice called out shrilly from the rocks ahead.
 They feared the Ancients.
 They had lost too many to continue fighting.  They were warned not to by Altha.  They feared the Ancients.  They knew they were losing the battle.