1972 D Kennedy error? Planchet lamination defect?
Kurisu
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Just came out of a customer roll.
Always willing to put myself out there to learn something... so I'll go first...
At first glance I thought maybe struck through retained rim burr from the copper layer.
Now I'm thinking defective planchet with a lamination issue, because I'm not seeing any tearing or gouging from an impact or something.
Teach me something. Please 
Coins are Neato!
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5
Comments
Kinda looks like a copper strip lamination. Or more likely a strike through.
Perhaps a thin strip of the copper bent/flaked away from the edge when still a planchet.... and was then struck by the die? Looks like a neat find to me.
Nice defective planchet.
Definitely a rim burr. Essentially a sliver of metal was sheered, incompletely, from the rim. It was then struck into the reverse face of the coin and has since been retained. A less detailed explanation would be a defective planchet. There are a couple types of rim burrs; I’d recommend checking out error-ref.com to check out which type of burr that you have.