There are several varieties. The more common one from my personal experience is the die chip that caused a blob that looks like an "extra cactus leaf" partially covering the initials of the engraver (JFM - Joseph F. Menna) on the reverse. It is located at the base of the Saquaro cactus among the pear cactus, and resembles another "leaf" of the pear cactus. Another variety of the "extra cactus leaf" partially covers the "2" in 2008. The picture below is from a Google search where apparently a coin was found with both "extra cactus leaves". I have found around 8 of the first variety and only one of the second.
