Not Like The Others

Out of the four things on house musician Jonathan Coulton's list, try to figure out which one does not belong and why. His clues cover everything from nursery rhymes and wonders of the world, to a certain song by Mr. Rick Astley.

Source: http://www.npr.org/2013/06/28/196296870/not-like-the-others?ft=1&f=1008

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