Scale rot is a bacterial infection found in snakes, it's often caused by the enclosure being too high in humidity for extended periods of time. Like, high humidity to a point where the substrate is moist for example.
Can also be caused by the enclosure being dirty, when the animal has to slither through their own excrements....
Treatment is (usually) a trip to the vet, a betadine or similar solution treatment, and anti-bacterial medication prescribed by the vet
If you Google around a bit, there's a lot more and more scientific (but also contradicting, for some reason) information on it!
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