He waited until the two men had crept away; then, crushing the feeling of eeriness that affected him in spite of himself, he bent his head and went forward into the tunnel. There was at once a scurry of animals past his legs; he felt the furry coats and tails of rabbits brush his hands; but he went slowly forward, touching the wall at his right to guide himself, and wondering how long the tunnel was, and whether there was enough air to carry him through to the end. The atmosphere was stuffy, with mingled smells so nauseating that Harry quickened his pace, eager to escape into purer air again. He had not thought to count his steps when he first entered the tunnel, but began to do so after taking about a dozen. At the fortieth of his counting the wall to his right came to an end. He stopped, and, raising his hand above his head, found that it was not obstructed by the roof: he had evidently come to the end of the passage. He stood upright and listened; he could hear nothing. Extending his arms, he found that he was in a narrow passage. Max had said that the tunnel led below the keep: there must, then, be a staircase somewhere. Harry went cautiously forward, stopping at every few steps to listen, and placing his feet with great care to avoid coming unawares upon some obstacle. At length his foot touched what felt like a stone step in front of him; another moment, and he was sure he had come to the expected staircase. It was pitch dark; he mounted carefully, and found that the stairs wound round and round. He had just counted fifteen steps, when his head came into violent contact with something above. The blow brought tears to his eyes, and he rubbed his head vigorously, as he had been wont to do after a knock in his childish days. Feeling with his hands, he discovered that the staircase was roofed over with stone. It appeared to be a slab let down into sockets; yet no, on the left side there was a space of about a finger-width between the stone and the wall, on the right there was no such space. He paused; the stone was so broad that to lift it was clearly impossible; it had never been intended to be moved from below. He bent his head, hitched his left shoulder, and shoved hard against the stone. It did not yield by the smallest interval. For a moment he was puzzled. Then a possible explanation of the space between the stone and the wall at the left occurred to him. Perhaps the stone moved on a pivot? He went to the other side and set his right shoulder to it. At first he felt no yielding; but exerting all his strength he shoved again, the stone slowly gave, and with continued pressure moved over until it came to a vertical position, leaving space enough for his body to pass through. He ascended, keeping his hand on the stone to prevent it from falling back noisily into its place, clambered on to the floor above, let the stone carefully down, and stood up to collect himself before proceeding farther.