Wirt's Third Leg

Source
This item can be found in pirate chests such as the Captain's Chest in Lost Rigger Cove in Tanaris, (the reward from Cuergo's Gold (quest), and a  which can be found on Southsea Pirates.

Trivia
This item is a reference to Wirt, a character in Blizzard's Diablo series.
 * In Diablo I, Wirt is a peg-legged boy who sells rare items in the town of Tristram. He lost his leg in a demon attack.
 * In Diablo II, an item called "Wirt's Leg" can be taken from his body. This item can be used to open the Secret Cow Level.
 * In Warcraft III, there is a boss in the final alliance level called Butcher. He drops an item called Wirt's Other Leg.
 * Wirt's Third Leg is named after Wirt, an annoying vendor in Diablo I who would only sell you one expensive item--after you paid 50g to view it. His leg was amputated and replaced with a wooden leg after an attack on his village. In Diablo II, Wirt is dead and his corpse has a ton of gold (for taking all that money in Diablo I) as well as his leg, which is used to open the Secret Cow Level. In Diablo III, you'll need to buy Wirt's Bell as one of the steps to access the new secret level, Whimsyshire.

Related

 * There is no cow level
 * Wirt's Gambled Leg