This was in another thread, but further examination leads me to starting this as I have a different opinion about it now. I hope you can see a definite seperation of the rim and the beginning of the extra metal starting at the UNITED. This leads me to believe the die had deteriorated. In the second picture you can see it goes 3/4 of the way around the coin and ends at the E in cent.
I apologize, I should have put the year. It is a 1972. I also spelled separate wrong, I learned phonetically and I also pronounce it wrong.
It looks like a rolling machine damaged the coin, and a layer is peeling away around the perimeter of the coin. It's pretty easy to see what is happening under the word CENT.
A possibility, but what is happening at the word UNITED? In that area it is raised and not peeling, then it progresses all the way around to the word CENT getting worse as it goes.
I strongly suspect this is post-strike damage. The affected letters look puffy or flattened. The pattern of distortion is like nothing I've seen on a genuine error.