My first thought when I read your post was a live mouse did the damage. What size is the snake, and do you ever feed live mice?
Other than that, my other thought would be something sharp or abrasive inside the enclosure. What type of bedding are you using? What decorations are inside the enclosure?
Can you post photos of the nicks/abrasions? Its hard to diagnose without seeing them. For most minor, external wounds you should be able to use Betadine or Neosporin to facilitate healing and prevent infection. Be sure to keep the snake in a sterile environment on paper towels or newspaper. Good luck!
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Ronda Van Winkle
Northwest Herpetoculture