Umbridge drew her wand from her sleeve. "How very thoughtful of you, McClaggen; however, I do think you are out of time. The funny thing about polyjuice, McClaggen, is that you need a fresh source of hair. We know that Lestrange was impersonating Umbridge. We found McClaggen, the real  McClaggen, in Dolores Umbridge’s flat. If you aren’t Lestrange and you aren’t  really  McClaggen, that must mean you are - Dolores."