The joke is a play on words. Turpentine is a volatile pungent oil distilled from gum turpentine or pine wood, used in mixing paints and varnishes and in liniment.  Turpentine sounds similar to 'serpentine', so serpentine was used in its place.  Serpentine means to move left to right in a 'snake-like' movement pattern.
My brother told me that serpentine is what you use to get paint off a boa constrictor .