No one can tell for sure what you're looking at until you clean it up...it appears to be a wound of some sort that has substrate stuck on it...what we cannot tell from
the photo is whether or not it's a fresh wound or an old one. Either way, clean it up, keep snake on clean paper for now, & use either Neosporin ointment (only the
kind WITHOUT pain relief) or Betadine solution (aka Povidone-Iodine) as an antiseptic IF it's at all a fresh wound. It might just be an older healing wound (rat bite?)
that got damp, & then substrate stuck to it.