As you all know, The Ballad of the Goddess from The Legend of Zelda: Skyward Sword is in fact just Zelda's Lullaby played backwards. If you're just discovering this for the first time, We'll give you a minute to let you come to terms with it.
Done? OK, then catch your breath and prepare to be dazzled once more! The main theme for the upcoming Nintendo 3DS exclusive, The Legend of Zelda: A Link Between Worlds, also hides its own little secret. Played backwards, you can clearly hear a section of the Hyrule Castle theme from its spiritual predecessor, The Legend of Zelda: A Link to the Past. Pretty cool, huh?
Also, if you play Tingle's Theme in reverse, it summons a hateful demon from the seventh layer of Hell who will bring endless pain and suffering to the mortal world. This also works if you play it forwards.