That would be a post mint stain. Any harsh or mildly harsh chemical can cause that. Soda, coffee, etc.
That's not being a pest.. that's asking a valid question. I do agree with paddy though appears to be post mint damage/staining rather then an error. I'd give it a drop or 2 of verdicare which would kill the verdigris (those green spots) and possibly lift that stain.. or maybe not.
It was a fully brown cent that was mostly exposed to an acidic substance, probably soda. The patch is a small area that was not exposed.
You’re not a pest, just someone trying to learn. It’s a drain after it left the mint. And those spits or lines by the date and his chin are damage. If you look closely at the one to the left of the date you can see metal has been moved and pushed to the south side.
