The Mug and Cauldron
"Father Robards said sometimes, if someone ain't buried proper when they die, their spirit won't go to rest like it should. That's where you get ghosts, an' walkers like these, an' a few other kinds a undead.
"Most a the ones around now are left from the plague, 'bout forty years ago. Folks dyin' too fast to get 'em all buried."