 From 1679 , Philippe Rohr devotes an essay to the dead who chew their shrouds in their graves , subject resumed later by Otto in 1732 , and then by Michael Ranft in 1734 . The subject was based on the peculiar phenomenon that when digging up graves , it was discovered that some corpses had at some point either devoured the interior fabric of their coffin or their own limbs . This distinguishes the relationship between vampirism and nightmares which were believed that many cases of vampirism were simply illusions brought by the imagination . While in 1732 an anonymous writer calling itself " the doctor Weimar " discusses the non @-@ putrefaction of these creatures , from a theological point of <unk> in 1733 , Johann Christoph <unk> wrote a general treatise on vampirism and the Marquis d <unk> Boyer cites local cases . Theologians and clergymen are also addressing the topic . 
