Remember The Scarecrow, the villain in Batman Begins that made fear-inducing toxin? Well, his weapons may soon be a reality, thanks to Pentagon scientists who are trying to isolate and harness the chemical scent of fear:
Pheromones are chemicals released by animals as signals to their own kind: for sex, for territorial marking, and more. They're often detected in the olfactory membranes. But there's more to pheromones than attraction. Many animals have an alarm pheromone which is used to signal danger; aphids, for example, use it to cause their fellow lice to flee.
Now, the US Army is trying to track down and harness people's smell of fear. The military has backed a study on the "Identification and Isolation of Human Alarm Pheromones," which "focused on the Preliminary Identification of Steroids of Interest in Human Fear Sweat." The so-called "skydiving protocol" was the researchers' method of choice.
You can imagine what the "skydiving protocol" entails! Wired's Danger Room blog has more: http://blog.wired.com/defense/2008/01/pentagon-resear.html