Snow white ended up with the seven dwarves because they made a fortune at the racetrack. Not the usual "Oh, and she lived happily ever after with lovely Prince Charming, and the rainbow shone, and the birds sang and everything was just so annoyingly perfect..." No, this is something that can be both more linked to our everyday life, but on the other hand, way more farther from it. Now it was like "Oh, and then she stole the mirror just because and the dwarves made a fortune and she fell in love with them (or their money, either way) and then the lights fade out..." Yes, very funny because of the way it turns a childish story into a double sense and with balck humor story. But even though it can have the double sense, (and the images contribute a lot to this) and it might be "less fantastic" or "less childish", one does not go listening to stories about a woman who slept with seven little guys at the same time because they were rich. I mean, everything can happen, the rainbowish ending, or the... lovely alternative ending.
That is what I consider great about everything, you can mock about everything you want, and the way Roald Dahl arranges the stories in his Revolting Rhymes, and puts them together in a very "poetic" way, makes them even funnier. It is a very good joke.
Roald Dahl has a very particular ability to put words together to tell elegant rhyming jokes without having to speak them. That is what I can see from Revolting Rhymes.
Image from: http://www.liquorsnob.com/pictures/ho-white.jpg
