More than 50 optical illusions, many with interactive elements such as flaps and pop-ups. Learn how NOT to believe what you see with this book of eye-popping pop-up visual tricks. From the classic "which dot is bigger?" or "is this line straight?" illusions to the first-ever 3D trick to appear in a book, Optical Illusions is packed with picture puzzles. Optical Illusions will get you lifting flaps and turning tabs in your quest to see the truth behind the illusion - and the more you discover, the more impressive the illusion becomes.