Last month, I judged a middle school science fair. It's a great way to familiarize yourself with cutting-edge research, such as the effects of music on plant growth, or the effects of soda on plant growth, or the reasons budding young scientists should never, ever be allowed to own hamsters.

One student did a project about landfills. Her background research described the importance of preventing the release of certain chemicals into the atmosphere -- chemicals such as dihydrogen monoxide (DHMO).

I smiled when I read that. The "evils" of DHMO are part of a famous science hoax, a very funny one that supposedly began more than 20 years ago on the University of California, Santa Cruz, campus. It crops up every so often.

Propaganda opposing DHMO cites the substance's presence in acid rain, use in naval warfare, and the fact that professional athletes can become dependent on its performance-enhancing abilities. Seriously, you should conduct a Google search of DHMO if you haven't seen this list. It's even funnier than that YouTube video showing the dancing Christmas tree surprising the cat. (If you haven't figured out yet what dihydrogen monoxide is, write out the chemical formula. Really? Okay, it's water. Now go tear up your doctoral diploma.)

I used to use the dihydrogen monoxide hoax on the first day of a class I taught about the public perception of science. After distributing a DHMO "fact sheet" detailing its dangers, I'd ask the students to decide the fate of this chemical. Most semesters, between one-quarter and one-half of the students voted to regulate or ban outright the scary-sounding DHMO.

Credit: Hal Mayforth

These were college students. Mostly science majors. At Johns Hopkins University. Which must be a smart school because that's where they filmed The Social Network.

Hoaxes have infiltrated science for centuries, from fake fossils (Piltdown Man, archaeoraptor, Calaveras skull) to fake medical conditions (cello scrotum, the disappearing blonde gene) to fake animals (Ompax spatuloides, Pacific Northwest tree octopus, Labradoodle). We love them, and we hate them, because they illustrate failures of our most important tool: our skepticism.

When city officials go nuts after learning that there's DHMO in the water pipes (which happened in Bremerton, Washington, in 2004), we're amused. But when scientists are the ones duped, hoaxes show how easy it is for us to stop thinking like scientists for a moment -- in other words, to stop doing the most fundamental part of our jobs.

If you're bored in the lab today, I highly recommend devising and perpetrating a new hoax (the harmless kind, not the Wakefield or Hwang Woo-Suk kind). Here are some ideas about how to conduct a good science hoax:

- Attach the bones of something to the bones of something else. You have just created the missing link between those two species. "It's amazing!" you can announce. "I've discovered the skeleton of the mythical half-chimp, half-sturgeon!" (Do not, however, attach the bones of something to nothing. It's really not that impressive to declare, "I've discovered the skeleton of the mythical half-chimp!" Gross.)

- Claim that your unique object has some impressive attribute, such as size, age, or incompatibility with accepted chronology. A 12-foot-tall, 9000-year-old Sony PlayStation, for example.

- Make your hoax scary. People should resist the urge to investigate fully because, well, they don't know that the Manitoba Cypress of Demise inflicts syphilis on all who dare speak its name, but do they really want to take that chance?

- Ensure that your hoax defies some well-established scientific principle. Ideally, it should involve one or more of the following: virgin birth, spontaneous generation, perpetual motion, cold fusion, or adequate funding.

- Remove a key component to make your claim unverifiable. Darn it, you can say to the experts who want to carbon-date your unicorn fossil, it appears all of the carbon is gone!

- If you're not going to make the "discovery" yourself, enlist an unlikely discoverer. Everyone knows that those least likely to make headlines for uncovering fantastic truths are scientists. We publish highly detailed papers about fruit fly hormones and quantum whatevers, and that seems to entertain us just fine. Fantastic apes and swamp monsters? Not really our thing. You want the person who leaks the discovery to be a 10-year-old child, an affable grandma, or the type of person who says, "Me and my dog Stinky was a-walkin' in the swamps, when we saw somethin' we swore must-a been a swamp coyote." (Bonus points if "coyote" is pronounced in only two syllables.)

- Find "experts" to corroborate your findings. Luckily, because you've ostensibly revealed something no one has heard of before, anyone you talk to for 5 minutes instantly becomes more of an "expert" than anyone else in the world.

- Before announcing your find, don't forget to remove the quotation marks around words such as "expert" and "discovery." Delete winking emoticons, too.

- Submit your data to the two most reputable peer-reviewed journals in the world, which, of course, are Wikipedia and YouTube.

At the science fair, the judges decided that the first one of us to speak to the DHMO-fearing sixth-grader should tell her what DHMO is, in order to spare her further embarrassment. That happened to be me.

After she delivered a brief lecture on the dangers of DHMO, I asked, "Do you know another name for DHMO?" She said she didn't. So I wrote the chemical formula "H2O" on the back of my judging sheet. She was unfazed.

"It's water," I explained. "Calling it DHMO is an old science joke -- your poster is saying that it's bad to have water in the atmosphere."

Again no shame. Instead, the student looked at me and said, defiantly, "Well, that's what my research found, so ..."

She said "so" in a way that meant, "The Internet said one thing, and if you disagree, then I guess it's just a difference of scientific opinion, so how can I be expected to know what to believe?"

And that's the problem with hoaxes. They can take on a life of their own, sitting on the Web in all their well-faked glory, waiting for someone to read them and cite them as truth. They can even open with a disclaimer that reads "THIS IS FAKE, EVERYBODY!" and people will still wonder if the disclaimer, not the hoax, is false.

When did skepticism become a bad thing? The public often accuses scientists of being overly skeptical, of the narrow-mindedness of believing only what we see and hear, or of haughtily dismissing skepticism's opposite, faith. (On a side note, I recently learned that there are actually skeptics conventions. Those sound like they'd be pretty confusing: "This afternoon's seminar will begin at 3:00. Or will it?")

But the truth is, we're not as skeptical as we portray ourselves to be. We believe things simply because they're relayed to us by other scientists. We believe what we read in journals, and we believe what our teachers tell us. We believe in subatomic particles we can't see. We're told that an instrument measures these particles, we can see the output of the instrument, we can understand the theory, and we can learn how the instrument works -- but that's as close as we can come.

And here we have no choice. We have to attribute validity to certain sources because we just don't know enough about every branch of science ourselves. Which is why, when one of those sources is debunked, we're deeply shaken. We remember how flimsy the foundation of our understanding really is. And that's scary, though maybe not as scary as the Manitoba Cypress of Demise.

So go, create your hoaxes and see whom you fool. Expose the gaps in our scientific rigor. If nothing else, you'll make it easier to judge middle school science fairs.

Hey, what's this poison gas wafting from the direction of Grover's Mill, New Jersey?

Adam Ruben, Ph.D., is a practicing scientist and the author of Surviving Your Stupid, Stupid Decision to Go to Grad School.

Adam Ruben, Ph.D., is a practicing scientist and the author of Surviving Your Stupid, Stupid Decision to Go to Grad School.