He held down the lamp to the floor, and as he did so I saw for the second time that night a startled, surprised look come over his face. For myself, as I followed his gaze, my skin was cold under my clothes. The floor was covered thickly with the prints of a naked foot – clear, well-defined, perfectly formed, but scarce half the size of those of an ordinary man.

"Holmes," I said in a whisper, "a child has done this horrid thing."

He had recovered his self-possession in an instant.

"I was staggered for the moment," he said, "but the thing is quite natural. My memory failed me, or I should have been able to foretell it. There is nothing more to be learned here. Let us go down."

"What is your theory, then, as to those footmarks?" I asked eagerly when we had regained the lower room once more.

"My dear Watson, try a little analysis yourself," said he with a touch of impatience. "You know my methods. Apply them, and it will be instructive to compare results."

"I cannot conceive anything which will cover the facts," I answered.

"It will be clear enough to you soon," he said, in an offhand way. "I think that there is nothing else of importance here, but I will look."

He whipped out his lens and a tape measure and hurried about the room on his knees, measuring, comparing, examining, with his long thin nose only a few inches from the planks and his beady eyes gleaming and deep-set like those of a bird. So swift, silent, and furtive were his movements, like those of a trained bloodhound picking out a scent, that I could not but think what a terrible criminal he would have made had he turned his energy and sagacity against the law instead of exerting them in its defence. As he hunted about, he kept muttering to himself, and finally he broke out into a loud crow of delight.