Here are some beliefs that might be true.
1.) Flowers were said to help a spirit accept that it was dead, so flowers were laid on graves.
2.) Graves were dug deep, so that the heavy earth piled on top of the coffins would keep the corpses in.
3.) Graves were clearly marked, as walking over a grave might make the body into a vampire.
4.) Heavy gravestones helped stop corpses from climbing out again.