a bitter - tasting water - soluble compound is dissolved in a non - polar substrate , imparting a bitter flavor to the substrate . this bitter flavor discourages rodents from gnawing on an object formed from the treated substrate . specifically , denatonium benzoate dissolves in molten flexible polyvinyl chloride , imparting a bitter taste to the plastic matrix . objects formed from this embittered plastic matrix are granted a degree of immunity from the predations of chewing animals ; rodents in particular .