    An invisible sign of his dead mother’s love? As much as Harry wished to scoff at the fanciful explanation, he had no idea of anything else that could explain why Quirrell had been unable to touch him. Instead, he nodded, dropping his face into a posture he knew made him look like he was upset. When Harry looked up, pretending to have collected himself, Professor Dumbledore was looking out the nearby window, studying a dull brown bird, a half-smile on his face as it warbled.