 Why is the Sand God causing a terrible storm?
The sand-thing was powerful, lonely and strange. A gray, funnel-shaped cloud of dust stood off to his left. Weather control made cyclones and other climatic phenomena on earth practically non-existent. The cloud did not move, though, except to spin on its axis rapidly, emitting a high-pitched, scarcely audible whine, like a high speed motor. Dark clouds capped one peak of the mountains on his left. He was here and Earth was somewhere up there. The sun burned fiercely, although he would have said it was about four o'clock in the afternoon, if this had been Earth. He was here to investigate, to determine if this planet was capable of supporting life. He examined the wind devil as closely as he dared, but it was composed only of grains of sand. But then, how could a group of loosely spaced grains of sand possibly have a nervous system? He became so absorbed in doing this that he failed to notice how the wind devil drew closer and closer, but when he inhaled the first grains of sand, the realization of what was happening dawned with a flash of fear. As he stood beside a small creek, a chill wind blew from the northwest. There, at the cavern entrance, the wind devil writhed and undulated in a brilliant harmony of colors. It came from the ceiling, the floor, the walls, the steaming pool. These are the undesirables, the incorrigibles, the nonconformists from the sixth planet.
 He is angry because he doesn't understand Stinson.
 He knows he can't control Stinson.  He is angry because Stinson figured out he is a child.  He is angry Stinson took Sybtl away from the webfoots.  He is angry because he doesn't understand Stinson.