After completion of this puzzle by Dutch designer, Oskar, the words 'key' and 'ring' should be properly lined up with each other. This is vital. If you try to put the pieces back together without lining up the words correctly, you will have failed even after achieving what appears at first to be a successful matching. It should read 'Key Ring' even when upside down. The wording design is courtesy of the prodigy, Scott Kim. The key word is 'pair'.