What is the 2005 buffalo nickel error?

Numerous buffalo nickels from the 2005 run depict an unusual error that makes one leg of the bison appear to be detached from the animal's body. Abrasions on the die used to cast the nickels caused the error, which made the nickels initially more valuable.

Although these buffalo nickels seem rare, there are actually quite a few nickels from the 2005 series that depict the error. The detached leg phenomenon is one of several caused by abrasions on the die from the use of abrasive cleaning agents. Another similar imperfection caused by a damaged die is the appearance of a ghostly spear through the body of some buffalo on other 2005 issue nickels.