Moving Pictures (Discworld #10)

People might say that reality is a quality that things possess in the same way that they possess weight. Sadly alchemists never really held with such a quaint notion. They think that they can change reality, shape it to their own purpose. Imagine then the damage that could be wrought if they get their hands on the ultimate alchemy: the invention of motion pictures, the greatest making of illusions. It may be a triumph of universe-shaking proportions. It's either that or they're about to unlock the dark terrible secret of the Holy Wood hills - by mistake...