Draco deliberately did a double take and let her catch him checking her out. If she'd put that much work into her appearance it was, after all, only polite to let her know it was the success it was.

And he met her smile with one of his own. "Do you indeed? When we're both capable of brewing polyjuice?" His smile widened into a smirk. "How do you know without it that I'm really me and not Mili Bulstrode or Greg Goyle?" Possibly because that wasn't the way either of them would have responded to a challenge like that.