The phrase Hair Of The Dog used to be “the hair of the dog that bit you”. Early English medical theory put forward that rubbing the hair of a dog into the wound of its bite would cure the ill effects it had caused and heal the wound. The phrase was used in many contexts until becoming a hangover remedy. Nowadays, if you have a few more drinks the day after a big drinking session it is said to cure the effects of the hangover and this is what we call “the hair of the dog”.