§ Of Beren and Lúthien The Silmarillion

But Lúthien heard his song, and she sang in answer, as she came through the woods unlooked for. For Huan, consenting once more to be her steed, had borne her swiftly hard upon Beren's trail. Long he had pondered in his heart what counsel he could devise for the lightning of the peril of these two whom he loved. He turned aside therefore at Sauron's isle, as they ran northward again, and he took thence the ghastly wolf-hame of Draugluin, and the bat-fell of Thuringwethil. She was the messenger of Sauron, and was wont to fly in vampire's form to Angband; and her great fingered wings were barbed at each joint's end with and iron claw. Clad in these dreadful garments Huan and Lúthien ran through Taur-nu-Fuin, and all things fled before them.