Optical Illusions is a fun and unique way to get the mental exercise you need. Use observation and visual reasoning skills in order to unlock the tricks behind these illusions. Use observation and visual reasoning skills in order to unlock the tricks behind these illusions. Great size for travel: 7-1/8 x 5-1/2 x 7/8 inches. Answer key in the back of the book. Spiral bound so the book can lie flat for full enjoyment. 256 pages