The borders between 40 countries are flipped horizontally and vertically (or rotated 180). Adding on top of that, each border lines up with all the other borders. This quiz will test your familiarity with the world map.
Once you find a flipped border, type in the 2 corresponding country names in the input box (both countries are required)
If at least one of the countries are named, then the associated border will turn green, even though you need the other country's name.