i have had 35% on my skin and it turned white, but did not hurt me. i rinsed it with water and the white eventually disappeared. not a recommended circumstance, but it is not the end of the world.
i say mix some of it with water till you should have a 3% concentration and then rinse your mouth with it. it should bubble up in your mouth and then spit it out. or, spit on a clean ceramic or glass plate and put a drop on it and see if it fizzes. no animal testing required.