 Why does Forbes want to take Purnie?
With everything around him in a state of perfect tableau, Purnie hurried toward the ocean. With it under his arm he bounded along a dozen more steps, then stopped abruptly in his tracks. 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. The tripon thought Purnie's feat was superb. Sure, it's your money that put us here; it's your expedition all the way. Purnie shrieked with joy at this new frolic and promptly stood on his head.
 Forbes wants Purnie because he emits radiation.
 Forbes wants Purnie because he emits radiation.  Forbes wants Purnie because he is very strong.  Forbes wants Purnie because he can stop time.  Forbes wants Purnie because he looks like a kangaroo.