Right from the Romantic period in the 19th Century, when there was widespread fascination with Eastern European "vampyrs", the vampire has been a "pathos-filled creature who has been at odds with his ontology and his innate desires, and who has struggled with them", says Williamson.

BBC: How vampires got all touchy-feely

Scores reflecting participants' views of how sacred their romantic relationships were changed during the four-week period as well.

ECONOMIST: Praying for your partner stops you straying