He had no idea who this Mistress was, but the human's first-hand experience with old magic was startling. He knew what it looked like, what it felt like, what it smelled like. He even knew what it looked like when a pony was using it up close and in detail. He told him enough, just enough so as to not arouse suspicion. He thought over the times he had personally used it and when, then thinking about what that would look like had he witnessed such things from his home on the boardwalk or at other parts of the harbour. He tried to conserve as much detail as he could so that he'd not make it seem like he had too much familiarity with the magic.