I voted for Oo. The coin was probably left in the ground or in some acid for a while. Definitely not a mint error.
Totally a damaged coin worth exactly ten cents. I noted Oo as it was the closest thing to Oh no look at that poor thing.
It's definitely damaged. Now the real question is whether it's a 1946-64 silver coin or a 1965-later clad. @Reggb- what does the edge look like? If it's a silver coin, it's worth a about a buck by today's melt price for silver. Clad, it's only worth ten cents. I voted "Oo", too, but then when I realized multiple votes were allowed in the poll, I went for "I" and "O" as well, just to cover all my bases.