That night we waited in darkness in Julia's room. Holmes had told me to bring my revolver. We sat without a light and without a sound for hours, listening to the church clock. Suddenly there was a gleam of light in the ventilator, and we smelled burning oil and heated metal: someone had lit a lantern in the next room. Then, about half past three, we heard a very gentle sound, like a small jet of steam escaping. In an instant Holmes sprang from the bed, struck a match, and lashed savagely with his cane at the bell-rope. "You see it, Watson?" he cried. "You see it?" I saw nothing, but I heard a low, clear whistle. Then a horrible cry broke out in the next room. We ran there. On a wooden chair sat Dr. Roylott, and round his head was a strange yellow band with brown speckles. It was a swamp adder, the deadliest snake in India. He had trained it to return through the ventilator, and that night it had turned upon its master.