People have been asking if we are going to do a more advanced book. Sometimes we think about it, but we think the easy stuff is just as much fun. Once you know the basic twists from our book, you can actually get the grown-up books and learn a lot more.
We found that when you first start twisting, those books are too hard to understand. That's why we made ours! But once you've got the basics, you can move on to the harder books much easier.