What's wrong with this nickle?

Hello again, I was wondering if anyone knows what's wrong with this coin. Is it cause by damage or wear? Is it a mistake? What happened here?!



Thanks,
Patrick

No one?  

Heavily worn, yes. Error, no. Just looks like someone dropped it and it laid there till someone picked it up months/years later.

Why, though? 1964 is a very common year for nickels. I find it a lot in rolls.

It looks like it was underground for some time.

Wasn't really looking for anything valueable, just curious about the type of damage and how it could be caused.  

Thank you for the replies!