"We did as you said, father," he answered. "We walked to the edge of the canal, and we walked back. We had no water and we had no air. We did not feel tired. We did not feel sick." "Fine! Fine!" murmured Goat. "Father ..." said Brute. Goat turned his eyes to Brute, and savage irritation swept over him. With that word, at that moment, Brute gave him a feeling of guilty foreboding. "Don't call me 'father!'" snapped Goat angrily. "But you say call you father," protested Brute, the puzzled frown wrinkling his brow. "What I call you if I not call you father?" "Don't call me anything. Say 'sir.' What did you want to say?" "Father, sir," began Brute again, "Adam forget. Adam fall." With a muted roar, Adam swept his powerful arm in a backhanded arc that caught Brute full on the side of his head. The blow would have felled an ox, but Brute was not shaken. Apparently unhurt, he stood patiently, his blue eyes on Goat with something of pleading in them. "Adam, let him alone!" commanded Goat sharply. "Brute, what do you mean, Adam fell?" "We come back. We not far from canal. Adam fall. Adam sick. Adam turn blue." "It is lies, father!" exclaimed Adam, glaring at Brute. "It is not true." "Let him finish," instructed Goat. "I'll decide whether it's true. What did you do, Brute?" "I find cactus, father," answered Brute. "I make hole in cactus. I put Adam inside. I put hole back. Adam stay in cactus. Then Adam break cactus and come out again. We come back." Goat cogitated. If Adam had shown, symptoms of oxygen starvation.... The big canal cacti were hollow, and in their interiors they maintained reserves of oxygen for their own use. More than once, such a cactus had saved a Martian traveler's life when his oxygen supply ran short. He turned to Adam. "Well, Adam?" he asked. "I tell you, father, it is lies! I do not fall. Brute does not put me in the cactus." "And why should he lie?" asked Goat blandly. This stumped Adam for a minute. Then he brightened. "Brute wants to be bigger and stronger than Adam," he said. "Brute knows Adam is bigger and stronger than Brute, Brute does not like this. He tells you lies so you will think Brute is bigger and stronger than Adam." "I know you are bigger brother, Adam," objected Brute, almost plaintively. "I not try to be bigger. Why you say you do not fall?" "I do not fall!" howled Adam. "I do not fall, you stupid Brute!" Goat held up a stern hand, enforcing silence. "I can't certainly settle this disagreement, but I'd be inclined to accept what Brute says," said Goat thoughtfully. "You're smart enough to lie, Adam. Brute isn't. The only thing I can do is to run the experiment over. You shall go out again tomorrow, and this time I'll go with you." "You'll see, father," said Adam confidently. "Adam will not fall." "Perhaps not. But I must be sure. As much as I prefer your more human characteristics, Adam, it's entirely possible that Brute has some survival qualities that you lack."