Back before we had a treatment for rabies, you had to catch the dog that bit you and put a bit of its hair into a potion. The thinking was that having a little hair of what caused you pain could magically cure you, kind of like a day-after flu vaccine. Magical thinking prevails in the advice that a shot of alcohol in the morning will cure a hangover (Carrie Fisher’s alcohol soaked memoir is titled, “Magical Drinking”). Hence we say, “hair of the dog” when we repeat an action in miniature that got us in trouble the night before. In actuality a heavy drinker would be better off drinking water (they are usually dehydrated), and seeing a counselor (any hangover is a sign of a toxic relationship with booze), rather than taking something that delays their reentry to reality.
Moses might well have said, “hair of the dog,” or its yiddish equivalent, when the people of the Exodus were faced with snakes in the dessert. Moses had them cast a snake in bronze wrapped around a pole. People who were bit by poisonous snakes were told to look upon this snake, lifted up, and they would be cured (Numbers 21:4-9). In an unrelated bit of mythology, the Greek/Roman god of healing, Asclepius, had a pole with a snake around it, which today is the symbol for medicine. The truth behind the magical thinking is that the prayers of Moses brought forgiveness and healing to the people. In looking to the snake and pole, the people were meant to focus on their dependance upon God, and repent from the sins that had broken their faith.