‘Hair of the dog’, a phrase which I, whose 1st language isn’t even English, remember vividly (in Romanian you’d say ‘only a nail can remove another nail’) has its origins in:
The 1st century AD, when this dude, Pliny the Elder, an author/ naturalist/ philosopher and whatnot, believed that if you got bit by a rabid animal (say, a dog), you should be eating a part of said animal in order to, well, get cured.