 Why does Purnie save the humans?
With everything around him in a state of perfect tableau, Purnie hurried toward the ocean. Further down the beach was a pair of two-legged animals poised in mid-step, facing the spot where Purnie now stood. It was time itself that Purnie had stopped, not the world around him. He scampered around the rockpile and down the sandy cliff to meet the tripons who, to him, had just come to life. The tripon thought Purnie's feat was superb. Purnie ran from pillar to post, trying to see and do everything at once. Purnie shrieked with joy at this new frolic and promptly stood on his head.
 Purnie blames himself for the avalanche that trapped his friends.
 Purnie is worried other humans will come to his planet if he doesn't save this group.  Purnie blames himself for the avalanche that trapped his friends.  Purnie thinks the humans are his friends.  Purnie thinks the humans can cure his radiation poisoning.