On April 1, I announced the Second Annual Movie-Plot Threat Contest:

Your entry will be judged on the common item that the TSA has no choice but to ban, as well as the cleverness of the plot. It has to be realistic; no science fiction, please. And the write-up is critical; last year the best entries were the most entertaining to read.

Make the TSA ban wristwatches. Or laptop computers. Or polyester. Or zippers over three inches long. You get the idea.

Your goal: invent a terrorist plot to hijack or blow up an airplane with a commonly carried item as a key component. The component should be so critical to the plot that the TSA will have no choice but to ban the item once the plot is uncovered. I want to see a plot horrific and ridiculous, but just plausible enough to take seriously.

On June 5, I posted three semi-finalists out of the 334 comments:

Well, we have a winner. I can’t divulge the exact formula — because you’ll all hack the system next year — but it was a combination of my opinion, popular acclaim in blog comments, and the opinion of Tom Grant (the previous year’s winner).

I present to you: Butterflies and Beverages, posted by Ron:

It must have been a pretty meadow, Wilkes thought, just a day before. He tried to picture how it looked then: without the long, wide wound in the earth, without the charred and broken fuselage of the jet that gouged it out, before the rolling ground was strewn with papers and cushions and random bits of plastic and fabric and all the things inside the plane that lay like the confetti from a brief, fiery parade.

Yes, a nice little spot, just far enough from the airport’s runways to be not too noisy, but close enough to watch the planes going in and out, fortunately just a bit too close to have been developed. When the plane rolled over and angled downward, not even a mile past the end of the runway, at least the only people at risk were the ones on the plane. For them, it was mercifully quick, the impact breaking their necks before the breaking wing tanks ignited in sheets of flame, the charred bodies still in their seats.

He spotted the NTSB guy, standing by the forward half of the fuselage, easy to spot among the FAA and local airport people — they were always the only suits in the crowd. Heading over, Wilkes saw this one wasn’t going to be too hard: when planes came down intact like this, breaking in to just a few pieces on impact, the cause was always easier to find. This one looked to be no exception.

He muttered to the suit, “Wilkes,” gesturing at the badge clipped to his shirt. No need to get too friendly, they’d file separate reports anyway. As long as they were remotely on the same page, there wasn’t much need to actually talk to the guy. “What’s this little gem?” he wondered aloud, looking at the hole in the side of the downed jet.

“Explosion,” drawled the NTSB guy; he had that Chuck Yeager slow-play sound, Wilkes thought, like someone who could sound calm describing Armageddon. “Looks like it was from the inside, something just big enough to rip a few square feet out of the side. Enough to throw it on its side”

“And if the plane is low enough, still taking off, with the engines near full thrust, it rolls over and down too fast…” he trailed off, picturing the result.

“Yep, all in a couple of seconds. Too quick for the flight crew to have time to get it back.” The NTSB guy shook his head, the id clipped to his suit jacket swaying back and forth with the motion. “Always the best time if you’re going to take a bird down: takeoff or landing, guess whoever did this one wanted to get it over with sooner rather than later.” He snorted in derision, “Somebody snuck in an explosive, must have been a screener havin’ an off day.”

“Maybe,” said Wilkes, not ready to write it off as just a screener’s error. The NTSB guys were always quick to find a bad decision, one human error, and explain the whole thing away. But Wilkes’ job was to find the flaws in the systems, the procedures, the way to come up with prophylactic precautions. Maybe there was nothing more than a screener who didn’t spot a grenade or a stick of dynamite, something so obvious that there was nothing to do but chalk up a hundred and eighty three dead lives to one madman and one very bad TSA employee.

But maybe not. That’s when Wilkes spotted the first two of the butterflies. Bright yellow against the charred black of the burned wreckage, they seemed like the most incongruous things — and as he thought this, another appeared.

As they took photos and made measurements, more showed up — by ones and twos, a few flying away, but gradually building up to dozens over the course of the morning. Odd, the NTSB rep agreed, but nothing that tells us anything about the terrorist who brought down that plane.

Wilkes wasn’t so sure. Nature was handing out a big fat clue here, he was sure of that. What he wasn’t sure of was what in the hell it could possibly mean.

He leaned in close with the camera on his phone, getting some good close images of the colorful insects, emailing back to the office with a request to reach out to an expert. He needed a phone consult, someone who knew the behavior of this particular butterfly, someone who could put him on the right track.

Within minutes, his phone was buzzing, with a conference call already set up with a professor of entymology, and even better one local to the area; a local might know this bug better than an academic from a more prestigious, but distant university.

He was half-listening during the introductions, Wilkes wasn’t interested in this guy’s particulars, the regional team would have that all available if he needed it later. He just wanted answers.

“Pieridae,” the professor offered, “and all males, I’d bet.”

“Okay,” Wilkes answered, wondering if he this really would tell him anything. “Why are they all over my bomb hole?”

“I can’t be sure, but it must be something attracting them. These are commonly called ‘sulfur butterflies’, could there be sulfur on your wreckage?”

Yeah, Wilkes thought, this is looking like a wild goose chase. “No sulfur, we already did a quick chem test for it. Anything else these little fellas like?”

“Sure, but not something you’d be likely to find in a bomb — just sodium. They package it up with their sperm and deliver it to the female as an extra little bonus — sort of the flowers and candy of the butterfly world.”

“Okay, that’s…wow, the things I learn in this job. Sorry to bother you, sir, I guess it’s just…yeah, thanks.”

Butterfly sperm — now this might set a new record for useless trivia learned in a crash investigation. Unbelievable.

The NTSB guy wandered over, seeing Wilkes was off the phone. “Get anything from your expert?” he queried, trying and failing to suppress a grin. Wilkes suspected there would soon be a story going around the NTSB office about the FAA “butterfly guy”; ah well, better to be infamous than anonymous.

“Nah, not much. The little guys like sulfur,” Wilkes offered, seeing his counterpart give a cynical chuckle at that, “and sodium. Unless there was a whole lot of salt packed around the perp’s explosive, our little yellow friends are just a mystery.”

The NTSB rep got a funny look on his face, a faraway look. “Sodium. An explosive that leaves behind sodium. Well, that could be…”

They looked at each other, both heading to the same conclusion, both reluctant to get there. Wilkes said it first: “Sodium metal. Cheap, easy to get, it would have to be: sodium metal.”

“And easy,” the NTSB rep drawled, “to sneak on the plane. The stuff is soft, but you could fashion it in to any simple things: eyeglass frames, belt buckles, buttons, simple things the screeners would never be lookin’ at.”

“Wouldn’t take much,” Wilkes offered, an old college chemistry-class prank coming to mind. “An couple of ounces, that would be enough to blow out the side of a plane, enough for what we’re seeing here.”

“With the easiest trigger in the world,” the NTSB man added, putting words to the picture forming in Wilkes mind. A cup of water would be enough, just drop the sodium metal in to it and the chemical reaction would quickly release hydrogen gas, with enough heat generated as a byproduct of the reaction to ignite the gas. In just a second or two, you’d have an explosion strong enough to knock the side out of a plane.

“Sounds like a problem for you FAA boys,” his counterpart teased. “What ya gonna do, ban passengers from carrying more than a few grams of anything made of metal? ”

“No,” Wilkes shot back, “we can’t ban everything that could be made of sodium metal. Or all the other water-reactives,” he mused aloud, thinking of all the carbides, anhydrides, and alkali metals that would cover. “Too many ways to hide them, too many types to test for them all. No, it isn’t the metals we’ll have to ban.”

“Naw, you don’t mean,” the NTSB man stared in disbelief, his eyes growing wide. “You couldn’t, I mean, it’s the only other way but it’s ridiculous.”

“No, it’s not so ridiculous, it’s really the only way. We’re going to have to ban water, and anything containing a significant amount of water, from all passenger flights. It’s the only way, otherwise we could have planes dropping out of the sky every time someone is served a beverage.”