How does Will trick the Dust Witch?

Charles is at a bar when Mr. Dark shows up and asks the bartender if he has seen Will and Jim. Charles gets up and quietly leaves. He walks to right above the storm drain in which Will and Jim are hiding. He notices the boys, but just then Mr. Dark walks up. Charles stalls and feigns ignorance. The Dust Witch approaches, sensing the ground with her fingers. She seems to sense the boys below, but Charles blows smoke in her face and begins to speak loudly, distracting her. Mr. Dark walks away with the Dust Witch, and Charles tells the boys to meet him at the library.