Mr. Shiftlet was so shocked that for about a hundred feet he drove along slowly with the door stiff open. A cloud, the exact color of the boy’s hat and shaped like a turnip, had descended over the sun, and another, worse looking, crouched behind the car. Mr. Shiftlet felt that the rottenness of the world was about to engulf him. He raised his arm and let it fall again to his breast. “Oh Lord!” he prayed. “Break forth and wash the slime from this earth!”

The turnip continued slowly to descend. After a few minutes there was a guffawing peal of thunder from behind and fantastic raindrops, like tin-can tops, crashed over the rear of Mr. Shiftlet’s car.

Which is a metaphor?
The turnip continued slowly to descend.
...raindrops, like tin-can drops, crashed over the rear of Mr. Shiflet’s car.
Mr. Shiftlet felt that the rottenness of the world was about to engulf him.
He raised his arm and let it fall again to his breast.