My favourite related trick is to use cross viewing to solve find-the-difference puzzles. Set up so the two images (with slight differences) are next to each ot

My favourite related trick is to use cross viewing to solve find-the-difference puzzles. Set up so the two images (with slight differences) are next to each other, cross your eyes, and look for 'shimmering' spots - these are the differences between the images. It makes differences very easy to spot, which is pretty cool!