Pharrell's song 'Happy' is easily one of the biggest hits around right now. The song can basically get anyone one in a good mood, which you probably assumed by it't title. But when you change the key, 'Happy' instantly becomes a breakup song.

Now, I'm sure this is the case with a lot of music, but hearing it (especially for this song in particular) is crazy! I almost like it better the sad way, then the happy way. Take a listen for yourself!