only way i can figure peter getting a scar and actually keeping it, would be if he gets the virus that everyone seems to be getting now, and that fights with his healing power he got from claire, somehow leaving him unable to heal that certain part.
similar (this is a stretch) to deadpool, in marvel comics. he was given part of wolverine's healing factor, but because of his cancer, he keeps recreating his scarred skin, instead of fully healing.
just a thought, anyway
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