Hand the book to a spectator, inform the spectator that some images have text and some do not. Say "Let's keep things simple. Pick an image WITHOUT text and make sure that only you can see it. Concentrate, and study it." Wait a few seconds. Ask the spectator to close the book. Take the book and put is aside; maybe out of reach. At this point you can tell the spectator what image he or she is thinking of!
But wait there's more: Now you can repeat the effect this time using an image with text next to it, and the results are the same. You can even sketch your prediction in form of a word or illustration on a notepad. If you sketched something out, you can then ask the spectator what he or she is thinking, then reveal what's been written on the notepad! This makes for a stronger ending.
