1985 Cent RPM Or Cud

Both are the result of a split in the copper shell and subsequent corrosion of the zinc underneath. This is a very common occurrence.

A little correction, a Cud will ONLY form along the outside rim of a coin. The definition of such being that a piece of the die completely breaks off and the die continues minting coins. This can only happen along the edge of the die. A Cud can never form along the edge of a mintmark.