The presence of vampires throughout history, culminating in the writing of Bram Stoker's Dracula, literature's most famous bloodsucker.

The popularity of Dracula cemented the vampire into fiction and popular culture, and was supplemented by the invention of cinema. Between Dracula and its not-so-subtle clone Nosferatu, vampires became a horror movie staple.

The idea of the dead coming back to life haunted stories for centuries. Differing takes on the myth led to different monsters – resurrection through science created Frankenstein's monster, Egyptian mythology and mummified pharaohs led to reanimated mummies, and external forces of evil or radiation brought forth zombies.

The idea of a parallel world of the spirits has persisted since the beginning of civilization. Ghosts returning to earth, or remaining as echoes of the past, are explored in this episode.

Humans have always sought justification for the presence of evil in the world. Demons, in their various incarnations through religious descriptions, folklore, and literature, are often cited as the source.

Witches in popular culture have a particularly insidious origin–religious persecution. In later years, the image of a witch has evolved–both through pop culture, and greater religious freedom.