6Optical illusions happen when we perceive something that's not there or that appears to differ from reality. Scientists divide them into three different categories: optical, perceptual, and cognitive. Readers will be delighted to learn how all kinds of optical illusions work and how they can amaze their friends with the experiments in this entertaining volume. They'll learn how to make a sequence of drawings seem to come to life, how to make a drawing appear 3D, how to draw the "impossible" Penrose triangle, and much, much more. All activities and experiments are explained step by step through comprehensible and accessible text.