England is old and small, so about 1500 they started running out
of places to bury people. So they would dig up coffins and
would take the bones to a 'bone house' and reuse the grave.
When reopening these coffins, one out of 25 coffins were found to
have scratch marks on the inside and they realized they had been
buring people alive. So they thought they would tie a string on the
wrist of the corpse, lead it through the coffin and up through
the ground and tie it to a bell. Someone would have to sit out in
the graveyard all night 'graveyard shift' to listen for the bell; thus,
someone could be 'saved by the bell' or was considered a 'dead ringer'.