Ostension is a folkloristic concept that is a good example of the powerful effect of folklore on societies and on people's lives.
It's usually defined as "the unwitting acting out of shared narratives by a community." But here it's easier to show than to tell*.
In 1808, a chill fell over the tiny British town of Great Paxton, county Huntingdonshire. First, in late 1807, one woman came down with convulsions and was bedridden. A few months later, a girl fell through the ice in the local pond - though she survived, she came down with convulsions as well, and so did a third girl the next month. As was later revealed to the (horrified) parish priest, Father Nicholson, the general consensus in town was that the women were bewitched. So one girl's father did what anyone would have done in this situation - he boiled a bottle of his daughter's urine, with pins in the cork, to find out the culprit. After several repetitions of the charm, it was generally agreed upon that the culprit was an old woman named Ann Izzard. And she runs in terror to Father Nicholson, and he chastises everybody in one of his sermons, and nothing happens for a few weeks.
Then Ann and a friend go to market, and on the way home, the friend's wagon overturns. She charges Ann for magically upsetting the cart to spoil her goods. This whips the village into a frenzy, and a few days later, they come to the Izzard home at night, drag Ann out of bed naked, lacerate her with pins, bruise her with her door-bar, and dash her head on the cobblestone road. She runs to the local constable, who refuses to defend her as he's not sworn in. She runs to a friend's house, and she protects her, but the friend later "discovers" that someone who houses a witch is as bad as the witch herself, neither eats nor sleeps, and dies a week later. It takes a second attack the next night and a village resolution to duck her the next morning to convince her to hide in Father Nicholson's house, where he is condemned by "eleven out of twelve" parishioners.
Father Nicholson delivers another hellfire sermon, citing 1 Samuel 28:7-24, and the foolishness of believing in witchcraft. This calms the village down enough for legal proceedings to continue. Nine are convicted, and two jailed later for a further attack on Ann. The Enlightenment-era judges are appalled by the events, while the defendants don't seem to understand what's wrong - after all, drawing blood from the witch stopped their daughters' convulsions. Ann moves to the outskirts of town and dies unhappy at the age of 93. Father Nicholson writes all this down and becomes our primary source for this story (Mitchell, 2000).
As unsettling as this may be, it's most striking that the villagers' actions were almost entirely sourced in shared narratives. They knew that a witch was causing their problems, and they knew how to find the witch, and how to tell she was a witch, and what to do with her - from folktales they had told and been told for centuries.
What's more, ostension is still a powerful force today. In Zimbabwe, for instance, the relatively new scare of HIV has coupled with the relatively old scare of albinism (it is widely believed throughout South Africa that the organs of albinos have magical properties) to create a new legend: that having sex with an albino woman will cure a man's HIV. This has led to many cases of rape (Machipisa, 2009).
In America, and especially in the late 1980's, ostension manifests itself in the form of rumor panics, most frequently as rumors of Satanic cult worshippers planning to murder high schoolers on prom night. There is, of course, no evidence for this - maybe some kids wearing goth makeup - but phone trees are set up, the community gets on high alert, and even the police, just like that constable from Great Paxton, reinforce the rumors (Ellis, 1990).
Another, closely related concept is quasi-ostension, where legends are used to explain ambiguous events. So a murder actually happens and then the community blames it on Satanic cults. There's clearly a lot of overlap: Great Paxton's "discovery" of Ann Izzard was more quasi-ostensive, but their reaction was by-the-book ostension.
A final concept is pseudo-ostension, which entails knowingly reenacting shared narratives. Everyone's heard the story of a woman sleeping with men in order to give them HIV (or typhoid, or the plague, or whatever the current scare is). A woman wrote into Ebony magazine under the name "C.J." claiming to have done this. Then a woman called into a radio station under the same name, claiming to do the nasty for revenge against the man who gave her HIV. In reality, this was hoaxes and damned hoaxes, but the hoaxer did it to raise HIV awareness - and yes, the number of HIV tests at local clinics spiked ("AIDS", 2009).
And that's why you can use folklore as weaponry.
Yes, weaponry. In the 1980's (under Gorbachev, even!), the Soviet Union began spreading rumors in South America that Americans were on a campaign to seize their babies and steal their organs. Sounds innocuous enough - stupid, even - but anti-Americanism remains extremely high, largely because of these gut fears, and in 1994, a tourist was beaten to death in a bathroom in response to fears that she had stolen a child. Another woman was attacked on a bus and the U.S. Embassy had to send guards to protect her (Booth, 1994). It's not napalm, but at the rate at which rumors spread, you can turn an entire country sheet-white against some nameless oppressor with folklore.
If you ask me, that's more powerful than any ICBM.
- Booth, William. "Witch Hunt: Babies are Disappearing, Ugly Rumors Abound, and a Tourist's Life is at Stake." The Washington Post, 17 May 1994. http://tafkac.org/medical/organ.theft/baby.parts/guatemalan_baby_snatchers.html, 1 Dec 2009.
- Ellis, Bill. "The Devil-Worshippers at the Prom: Rumor-Panic as Therapeutic Magic." Western Folklore 49:1 (1990), pp. 27-49.
- Machipisa, Lewis. "Albinos hit by Zimbabwe's race divide." BBC News, 14 Jan 2003. http://news.bbc.co.uk/2/hi/africa/2646967.stm, 1 Dec 2009.
- Mitchell, Stephen A. "Witchcraft Persecutions in the Post-Craze Era: The Case of Ann Izzard of Great Paxton, 1808." Western Folklore, 59:3 (2000), pp. 304-328.
- "AIDS: Spreading Fear, Not Disease." Time, 4 Nov 1991. http://www.time.com/time/magazine/article/0,9171,974172,00.html, 1 Dec 2009.
*which is actually the other meaning of "ostension." Thanks, Oolong!