World's Most Difficult Jigsaw Puzzle

Last night I finally finished what is called the 'World's Most Difficult Jigsaw Puzzle'. Basically it's a puzzle made entirely of smiley faces. The difficult part comes in that while normal jigsaw puzzles have the picture on just one side of the piece, this one has it on both sides (with the opposite picture flipped 90 degrees). So you don't know if the side of the piece you are trying to work with goes in the top or the bottom. Also being that it's all smiley faces and nothing else doesn't help either. It took me a few weeks to finish it. A good thing to do when Liz is away and I don't currently have a TV.