Rob Dunn at GAS has "a sure-fire way to find all the differences in 'spot the difference' picture puzzles in a matter of seconds" as long as you can cross your eyes. First, set the pictures side by side. Then:
- Stare at the pictures, begin to cross your eyes.
- You should see a third image appear between the two pictures.
- Focus on the middle picture, adjusting the tilt of your head so both pictures line up exactly.
- Once you’ve focused on the image, all the differences should look “luminescent”.
Tell me if it works.
Image from AllStarPuzzles