I'm sure most, if not all, of you have read a MAD Magazine at some point in your life. Remember wgi they had that back page, where you would look at it and see one image, then fold it on the lines and get a whole new image? (Like this but vertical or horizontal folds instead diagnal.)
I wonder how hard it would be to make webapages that do the same thing. You would load the first page in one window, then open the proper page in the second window, line the windows up, and get a whole new and amusing page.