 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. The sun shone obliquely, throwing Stinson's shadow upon the sand. The wind devil also had a shadow, although the sun shone through it and the shadow was faint. 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. It is impossible to move a physical body from one place to another by a mere thought and a tiny instrument, yet you have done so. These are the undesirables, the incorrigibles, the nonconformists from the sixth planet. I see you as a cone of sand which keeps changing color and configuration. And this is contrary to the greatest law of all—that an entity, once in existence, can never cease to exist." "Please ask the Sand God," she said, "to speak to my people again. "As for the webfoots," the wind devil, or Sand God, said, "I will destroy them. It has to do with what comes after physical existence, not with existence itself. The greatest law is this, that an entity, once existing, must not be harmed in any way. To do so changes the most basic structure of nature." The Sand God did not reply.
 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.