Foreshadowing is something that is used in fables and folk literature quite usually, often to emphasize the moral of story even before it is explicitly stated in the end. Because of that, the reader or listener focuses his attention on what will eventually be the point of the story, making it more believable.
Roald Dahl’s version of Cinderella is no exception. He starts the fable, ‘I guess you think you know this story. / You don’t. The real one’s much more gory.’ The reader is instantly intrigued, since he knows what to expect, but too remotely to understand what the moral of the story will be. It is only clear that Dahl will eventually lead up to the original narrative being too naïve and conventional and add new features to the classic fable. ‘The phoney one, the one you know, / Was cooked up years and years ago, / And made to sound all soft and sappy just to keep the children happy.’ – he elaborates on the point.
The rest of the story is told predictably until the climax of the story, when the prince decapitates the Ugly Sisters. The moral is not stated openly as it was in the original Charles Perrault’s version, but it is transparent what Dahl means to say. His moral is just as simple: one should not be so innocent to believe in children’s fables, but rather base his or her understanding of life on the worst case scenario.
Reference: all quotations taken from Roald Dahl, “Roald Dahl’s Revolting rhymes”, Knopf, 1983.