She repaid him for his compliment by smiling in a peculiar, secret way and running her tongue over her lips. It was one of her most characteristic gestures and very effective. It seemed to promise all sorts of undefined intimacies, yet it was really as simple and automatic as the word thanks. She used it to reward anyone for anything, no matter how unimportant.
This passage appears in Chapter 22 while Faye is preening for Claude and the other men after the cockfight. This particular moment encapsulates the many social moments in The Day of the Locust that hinge upon misunderstanding and misreading. Here, the problem is Faye's inability to consider her audience's reception of her acting, combined with Claude's inability to remain objective about her. In Chapter 15, Tod marvels at Harry's inability to express subtle feelings. Such a lack of nuance reappears at this moment in Faye, as she has no refined sense of when or with whom her seemingly intimate smile would be appropriate. The mechanical nature of Faye's artificiality, therefore, opens up a possibility for misunderstanding, which in turn leads to embittered feelings that can escalate to violence.