the fat man, who was nearer. Slowly it gathered itself to spring.

Wallace shrugged off Al-fin's hand, that still rested on his, just as the cat left its feet. He had no chance to fire. The cat finished its spring—and the ground caved in beneath its feet. A moment later they heard its snarling and spitting from several yards underground.

Calmly, unhurriedly, the natives picked boulders from the ground and carried them to the pit. They dropped or threw them down on the cat until its snarls changed from anger to pain, and died completely.

Wallace and Saxton walked to the edge of the pit and looked down. The cat was dead. Its carcass lay sprawled over those of another dozen of its kind.

"Evidently they've used this method often before," Wallace remarked. A thought occurred to him and he looked at Saxton.

Saxton nodded in unspoken agreement. "We've just seen another demonstration of that ability we're trying to find," he said.

"But what is it?" Wallace asked.

"Can it be anything except acute hearing?"

"If it was only that, how did they know where the cat would appear, and what it would do? If it had circled the pit they would have been helpless. Yet they did nothing except retreat to the far side of the clearing and wait."

Saxton shook his head in defeat. "They did act with plenty of assurance—but how did they know? Do you think we should stay around some more, and watch how they operate?"

Wallace glanced up at the rapidly moving sun. "We'd better get back to the ship," he said. "We have only about enough time to reach it before dark. We can come back again tomorrow, if you want."

That evening as he lay on his bunk, Wallace noted that Saxton was growing restless again. Their being unable to find a way to evade the bloodhound was bringing the irritable part of his nature to the surface. The time had come again to furnish diversion. "I'm sure we have all the clues on those savages," he said. "If we just understood how to fit them together."

It worked. Saxton stopped pacing and bared his teeth in a smile. "You still think they developed some special ability, don't you?" he asked. "I don't agree. Nineteen hundred years—the time the colony's been here—is too short for any change to take place. Evolution doesn't work that 

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