This was always my favorite thing in Mad magazine. One page (the inside of the back cover, I think) was covered in a zany illustration. You folded that page in thirds, covering up the middle-third of that image, and a new image would form because the illustration was designed to perfectly line up with those folds. The new image (and text!) was part of the joke.
Every one was a clever trick, so of course, I’m delighted to see that … Read article “The Mad Magazine Fold-In Effect in CSS”