"He hurriedly slipped the money in his waist, his lone eye darting side to side"

The way Hosseini uses imagery to portray the man's actions shows us that the man is cautious after being given the money. In a place where the government is violent and disorganized, it is probably not the best idea to be seen with a lot of money. When Hosseini says "his lone eye darting side to side," it conveys the man's nervousness in being seen with the money, and he looks around to see if anyone has seen him with the money, as well as to keep it safe.