SD Alcohol 40, the alcohol in mouthwashes, is ethanol denatured with Denatonium Benzoate, which is toxic in high enough doses, although it is less toxic than methanol, and is relatively safe as a mouth rinse, unlike methanol, which is absorbed through intact skin and mucous membranes. Denatonium Benzoate also has a very bitter taste. I believe that mouthwashes also have an ingredient that is an emetic, that is, an ingredient that induces vomiting, to counter the toxic effects of ingesting it.