"Because I've used it several times over the years." He studied her face and the truth shining behind her eyes and he drew his head back. A silent conversation seemed to flow from them just then as Draco went back through his memory over the years. How she, Harry and Ron had sometimes been in places and heard things they shouldn't have been able to hear or see. How they sometimes knew things no other students should be able to know. Even despite Draco's close ties with certain professors.