 Why was Thig informed that he should be camouflaged as a human?
Here he patiently sat down to wait for an Earthman or an Earthwoman to pass. An hour later, his scars and altered cartilage already healed and painless, Thig again scraped sand over the entrance to the space ship and set out along the moonlit beach toward the nearest path running inland to his home. Men had no mates on Ortha, sex had been overthrown with all the other primitive impulses of barbarism; so he was incapable of understanding the emotions that swept through his acquired memory. Tonight or tomorrow night at the latest he must contact his two fellows and report that Earth was a planetary paradise. For three months he had lived with people who loved, hated, wept and sacrificed for reasons that he had never known existed.
 So that he could scout out the surroundings without suspicions
 So that he could scout out the surroundings without suspicions  So that he could learn the inner thoughts of humans.  So that no one would know that Lewis was taken.  So that he could impersonate Lewis and fool his family.