His words gave me matter for profound thought during my short vigil. I recalled the appearance of the dead woman very vividly--indeed, I am not likely ever to forget it--and I strove to connect that appearance with his desire to examine the back of the corpse. But there seemed to be no connexion at all. The visible injuries were in front, and I had seen nothing to suggest the existence of any others. From time to time I tested the condition of the plaster, impatient to rejoin my colleague but fearful of cracking the thin cast by raising it prematurely. At length the plaster seemed to be hard enough, and trusting to the strength of the canvas, I prised cautiously at the edge, when, to my relief, the brittle plate came up safely and I lifted it clear. Wrapping it carefully in some spare rag, I packed it in the research-case, and then, taking this and the lantern, made my way back to the house. When I had let down the catch and closed the front door, I went into the drawing-room, where I found Thorndyke stooping over the dark stain at the threshold and scanning the floor as if in search of something. I reported the completion of the cast and then asked him what he was looking for. “I am looking for a button,” he replied. “There is one missing from the back; the one to which the collar was fastened.” “Is it of any importance?” I asked. “It is important to ascertain when and where it became detached,” he replied. “Let us have the inspection-lamp.” I gave him the lamp, which he placed on the floor, turning it so that its beam of light travelled along the surface. Stooping to follow the light, I scrutinized the floor minutely but in vain. “It may not be here at all,” said I; but at that moment the bright gleam, penetrating the darkness under a cabinet, struck a small object close to the wall. In a moment I had thrown myself prone on the carpet, and reaching under the cabinet, brought forth a largish mother-of-pearl button. “You notice,” said Thorndyke, as he examined it, “that the cabinet is near the window, at the opposite end of the room to the couch. But we had better see that it is the right button.” He walked slowly towards the couch, still stooping and searching the floor with the light. The corpse, I noticed, had been turned on its side, exposing the back and the displaced collar. Through the strained button-hole of the latter Thorndyke passed the button without difficulty. “Yes,” he said, “that is where it came from. You will notice that there is a similar one in front. By the way,” he continued, bringing the lamp close to the surface of the grey serge dress, “I picked off one or two hairs--animal hairs; cat and dog they looked like. Here are one or two more. Will you hold the lamp while I take them off?” “They are probably from some pets of hers,” I remarked, as he picked them off with his forceps and deposited them in one of the invaluable seed-envelopes. “Spinsters are a good deal addicted to pets, especially cats and dogs.”