Denatonium benzonate is a white crystalline powder with an extremely bitter taste. It gets its name from denatured alcohol, and that is where it is often used. It is the bitterest tasting substance known. Especially denatured alcohol 40, or SD-40, is ethanol denatured by a tiny amount denatonium benzoate. It is an ester of PABA, and is related to lidocaine, benzocaine, novocaine, and cocaine. It is used in deer repellant, nail polish, paints, antifreeze and windshield washing fluid, and to coat electrical cables to prevent rats from eating the insulation. Very dilute solutions are also used to coat children's thumbs to prevent thumb sucking.