 Why did Thig react with violence towards Kam while they were traveling back to Ortha?
"With a psychic relay we will transfer the Earthman's memories and meager store of knowledge to the brain of Thig! "For the good of the Horde," Thig intoned almost piously as he lifted Terry's body and headed for the laboratory. 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.
 He wanted to return to Earth and to Ellen.
 He wanted to return to Earth and to Ellen.  He did not want his blood tested for disease.  He was angry that they had killed Lewis.  He did not want to live on Earth any longer.