Quote from : The Graveyard Book Book

One grave in every graveyard belongs to the ghouls. Wander any graveyard long enough and you will find it - water stained and bulging, with cracked or broken stone, scraggly grass or rank weeds about it, and a feeling, when you reach it, of abandonment. It may be colder than the other gravestones, too, and the name on the stone is all too often impossible to read. If there is a statue on the grave it will be headless or so scabbed with fungus and lichens as to look like fungus itself. If one grave in a graveyard looks like a target for petty vandals, that is the ghoul-gate. If the grave wants to make you be somewhere else, that is the ghoul-gate.