Each optical teaser in this challenging book is a small diagram that, when stared at or moved in a certain way, tricks the eyes. Brief directions show readers how to experience the teaser. Some of these "directions" ask a question intended to make the viewer do something. The answer to the question is determined by viewing the teaser and is also printed in upside-down text at the bottom of the page. The teasers are very easy to perform but are interesting enough to merit repeated viewings. Includes over 80 puzzles.