Aziraphale doesn’t seem to realize that other children, like the little girl in this passage, are just as rude and dismissive as Warlock is. In other words, it’s possible that children, not just the supposed Antichrist, are “infernally tainted”—that is, that they have elements of evil in them. Meanwhile, the fact that Aziraphale dedicated a year of his life to learning real sleight of hand is humorous, given that he’s an angel with supernatural powers (for instance, the ability to remove alcohol from his blood in the previous chapter). But since he’s been assigned to live and work on Earth, he wants to learn skills through honest, hard work, the way human beings do—and as an immortal, he has the time to do so. Aziraphale, like Crowley, seems to find human pastimes endearing and enjoyable.