1981 P Dime Possible error

Hello everyone, I am far from having the knowledge to know what went wrong with this coin IF ANY. It Came out of a vending machine and automatically caught my eye.
The obverse side looks a bit normal, although when looking at the reverse, it seems to be very bold. I have attached the obverse and reverse sides of the coin. Please let me know your thoughts. If I need to take better pics I can do that. Thanks to all!

 

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Reverse looks normal to me. Maybe because it's dirty it makes it look that way.

 

I see a lot of what look to be flow lines as well.

 

Thanks Paddyman, the front is pretty dirty, although the reverse is actually pretty clean and very Bold. Which grabbed my attention. Thanks again!

 

Flurry, can you please explain how flow lines are created? In what area do you see the flow lines?

 

Not meaning to step on furry's post...On the reverse from the left branch across to the right branch, lines are radiating outwards towards the lettering. Also called striations and the result of a worn die, but not an error.

 

Thanks guys very helpful.