At first it was but a lurid spark upon the stone pavement. Then it lengthened out until it became a yellow line, and then, without any warning or sound, a gash seemed to open and a hand appeared, a white, almost womanly hand, which felt about in the centre of the little area of light. For a minute or more the hand, with its writhing fingers, protruded out of the floor. Then it was withdrawn as suddenly as it appeared, and all was dark again save the single lurid spark which marked a chink between the stones.