In other words, give them something like the Internet — at least in theory.

Now let’s look at my experience with zombie panic and the Internet. Even before the “Coast to Coast” radio broadcast, it didn’t take much to find evidence online that I was already “warning” the nation about zombies. I had written a fake medical paper on the putative virus that causes zombification, so there was ample evidence to confirm your worst fears of zombies — assuming you didn’t read any of the online reports about my paper (which were all in on the joke) too closely.

In fact, Ataxic Neurodegenerative Satiety Deficiency syndrome, the disease that I simply made up, now has its own Web site, and there are supposed photos of A.N.S.D. that you can find through a Google search. (I did not know about any of this until my wife showed it to me.) Drexel University once ran a disaster drill for nurses using an outbreak of A.N.S.D. as a model, and the C.D.C. mentioned A.N.S.D. in its own blog.

So much for using the Internet to defuse panic. In some ways, the same method that our policy makers recommended indirectly back in 1938 has heightened our capacity for social hysteria. You can find evidence for nearly anything that scares you if you simply look for that evidence online. An illegitimate president fudging his birth records? A grand conspiracy to topple the twin towers and blame terrorists? A frightening link between vaccines and illnesses? “Proof” of all this and more is only a Google search away.

Social psychologists note that in game situations, the more outlandish the bluff, the more likely it is that the bluff is taken seriously. The human interpretation of a giant fib seems to be that the apparent mistruth wouldn’t be worth telling — that being caught in the lie would not be worth the risk of being caught — unless the lie were in fact true. As the mathematician Blaise Pascal once said, “We want to be deceived.”

To be sure, conspiracy myths and mass hysteria were not invented with the Internet. But the online world allows a tiny spore of ridiculous conjecture to mushroom quickly into a widely disseminated belief. This happens, in part, because you often go to the Internet to look for information that confirms your pre-existing mythologies. This is what social and cognitive psychologists call “confirmation bias” — the idea that, if you have a preconception, you will selectively examine the available evidence to support that belief. Perhaps worse, you will selectively ignore the evidence that challenges your convictions.

The Internet is in many ways designed to amplify this bias — not just temperamentally but technically. For example, if you use my computer to search the word “food,” the very first jpeg that a Google Images search yields is an electron micrograph of salmonella. But if I were to use someone else’s laptop — someone who didn’t use his computer to write about zombies and infection and food-borne illness — I’d more likely get a photograph of pizza or a salad. To this end, the Internet recycles your own preconceptions, even in the guise of a seemingly random inquiry. It scares you with what it thinks you want to know.

There are other aspects of media-generated hoaxes and panic that are worth noting. Those who studied the “War of the Worlds” fiasco noted that the apparent authority of a well-known figure like Orson Welles, coupled with the modality of radio (the major means by which information was transmitted at the time), lent credibility to what would otherwise have been received as science fiction. (Imagine, by contrast, if a random person ran screaming toward you on the street, saying that Mars was invading Earth.) Additionally, the Great Depression and the looming, free-floating anxiety of World War II proved to be fertile soil for panic. The public was waiting for something in which they could situate their already present fears.