"Actually, you did. Quite advanced Magic. Two-way notebooks are pretty common. You can buy them from Flourish and Blotts. But ours, no one can read the messages except for us, which is useful if one of us gets captured or—Even a Revelio doesn’t work on it. The ink is tied to our Magical signatures. Anyway, I always knew you were an exceptional Witch," Malfoy explained. 