I don't know how relevant it is, but just yesterday I came across this on the internet. Kind of gruesome, but interesting:

"SAVED BY THE BELL

[Q] From a lot of people - including Mike Whitling and Lisa Smith from the USA and Barrie J Wright from Australia: “The following is part of a longer piece that’s been making the rounds by e-mail in recent months. Is any of it true?

England is old and small and they started running out of places to bury people. So, they would dig up coffins and would take their bones to a house and re-use the grave. In reopening these coffins, one out of 25 coffins were found to have scratch marks on the inside and they realized they had been burying people alive. So they thought they would tie a string on their wrist and 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 to listen for the bell. Hence on the ‘graveyard shift’ they would know that someone was ‘saved by the bell’, or he was a ‘dead ringer’.”

[A] You may not be pleased to hear that all this is complete and utter hogwash, just like the rest of the article. It’s an example of a fascinating process (that is, from a sociolinguistic perspective) in which people actively seek out stories to explain phrases, not really caring whether they are true, just that they are psychologically satisfying. As a result, they are powerful memes, strongly resisting refutation. But World Wide Words is renowned as the home of lost causes, so I’ll give it a go.

Saved by the bell is actually boxing slang, dating from the 1930s. A contestant being counted out might be saved by the ringing of the bell for the end of the round, giving him a minute to recover. Graveyard shift is an evocative term for the night shift between about midnight and eight in the morning, when—no matter how often you’ve worked it—your skin is clammy, there’s sand behind your eyeballs, and the world is creepily silent, like the graveyard (sailors similarly know the graveyard watch, the midnight to four a.m. stint). The phrase dates only from the early years of the twentieth century. The third phrase—dead ringer—dates from roughly the same period or perhaps a decade or two earlier. I’ve written about it previously, so won’t explain it again.

So none of these expressions has anything to do with the burying of bodies"

http://www.quinion.com/words/qa/qa-sav1.htm

Robert