 The systems using cords tied to the body suffered from the drawback that the natural processes of decay often caused the body to swell or shift position, causing accidental tension on the cords and a "false positive".Franz Vester's 1868 "Burial Case" overcame this problem by adding a tube through which the face of the "corpse" could be viewed.If the interred person came to, they could ring the bell (if not strong enough to ascend the tube by means of a supplied ladder) and the watchmen could check to see if the person had genuinely returned to life or whether it was merely a movement of the corpse.