Debbie dropped her luggage on the floor of the little efficiency apartment allocated to her in the Bradbury habitat on Mars and sneezed. The sound bounced back and forth from one wall to another, increasing in annoyance with each bounce. The apartment seemed spotless at first, but when she looked at the furniture, walls, and floors more carefully, she saw that they were covered with a light but uniformly thin layer of pinkish dust, possibly causing the subtle scent of pero