It's odd, being so localized. Definitely not a burn. Scale rot can be localized to individual scales, but doesn't just appear overnight. If you are 100% certain that a day or two ago, this wasn't present, look at the enclosure. What, if anything, could your python get to, that could damage the scales. Is there anything adhesive that it may have gotten stuck to, damaging the scales? Could this have happened the last time the snake was out?

In any case, I would switch to paper towel substrate during the healing process, and do soaks in diluted betadine. Also cover the area with polysporin (without the painkillers) and keep a close eye on things.

On a side note, since you have chlorhexidine, if you dilute it to 2% (the topical formulas are usually 4%), it makes for a fantastic antiseptic cleaner. I use it frequently with quarantined animals.

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