Until the high-velocity rounds began to pass down into their apartment from above, Marlon had never troubled himself to think about the possible drawbacks of having neighbors who shared his attitude about what constituted suitable real estate. He had the vague sense that the apartment above them was crowded, but that was frequently the case in buildings like this one. From time to time, as they climbed the stairs to play basketball on the roof, they would see people who seemed to be waidiren —"not from around here" types, internal foreigners—and perhaps even waiguoren —non-Chinese. If the wind was blowing the right way, they would sometimes get a whiff of chemical odors, but it was difficult to pin down their origin.