Cauterization would have to be applied immediately to have any chance of working. However, another mechanism comes to mind that would permit the existence of m

Cauterization would have to be applied immediately to have any chance of working. However, another mechanism comes to mind that would permit the existence of madstones: Note that they were often organic in nature and note the milk bit. I'm thinking of some very heat tolerant bacteria living in the material, boiling it in milk will give it a nutrient-rich liquid basically devoid of other pathogens. Suppose said bacteria exhibits a surface antigen matching some part of the rabies virus? You can make a vaccine by exhibiting the target structure on a harmless pathogen. (Case in point, Sputnik V. It's not usually done because such a vaccine also makes the patient immune to the vaccine--Sputnik V primary dose and booster dose were separate things because of this.) And how does a bacteria come to exhibit this? There's plenty of viral code embedded in our DNA, the same thing could happen to a bacteria. While this is obviously a low-probability scenario I don't see that it can be ruled out. There are an awful lot of pathogens out there that don't cause obvious symptoms and thus have never been studied. (Sometimes they cause non-obvious symptoms, though--think of HPV and cancer for the well-known case but there are others. Personally, I suspect that we have only scratched the surface on this.)