Quote:"Among the rarest of all errors are two-headed and two-tailed mules (mules are coins struck by mismatched dies)
Only one double-obverse ("two-headed") mule is known among U.S. coins — a 1859
Indian cent. Only three known double reverse ("two-tailed") mules are known — two copper-nickel clad quarter dollars and one copper-nickel clad dime." - Mike Diamond
Coin World 04/16/11
Note :According to Mr. Diamond, this coin also could be a
pseudo mule a thoroughly "Assisted Mint error" by a bit of mischief in a machine shop...