This is an archived article that was published on sltrib.com in 2016, and information in the article may be outdated. It is provided only for personal research purposes and may not be reprinted.

WASHINGTON • Last week, a 40-year-old man — with dark, curly hair, olive skin and an exotic foreign accent — boarded a plane. It was to make an uneventful hop from Philadelphia to nearby Syracuse.

Or so dozens of unsuspecting passengers thought.

The man kept to himself, intently if inscrutably scribbling on a notepad. His seatmate, a blond-haired, 30-something woman sporting flip-flops and a red tote bag, looked him over. He was wearing navy Diesel jeans and a red Lacoste sweater — a look he would later describe as "simple elegance" — but something about him didn't seem right to her.

She decided to try out some small talk.

Is Syracuse home? She asked.

No, he replied curtly.

He deflected further questions. He appeared laser-focused on those strange scribblings.

Rebuffed, the woman began reading her book. Or pretending to read, anyway. Shortly after boarding had finished, she handed the flight attendant a note.

Then the passengers waited. After they'd sat on the tarmac for about half an hour, the flight attendant approached the female passenger again and asked if she now felt OK to fly, or if she was "too sick."

I'm OK to fly, the woman responded.

She must not have sounded convincing, though; American Airlines flight 3950 remained grounded.

Then the plane returned to the gate, and the woman was escorted off the plane.

The wait continued.

Finally the pilot came by, approaching the real culprit behind the delay: that darkly complected foreign man. He was escorted off the plane, too, and taken to meet security personnel.

What do you know about your seatmate? An agent asked the man.

Well, she acted a bit funny, he replied, but she didn't seem visibly ill. Maybe, he thought, they wanted his help in piecing together what was wrong with her.

And then the big reveal: The woman wasn't really sick at all! Instead this quick-thinking traveler had Seen Something, and Said Something.

That Something she'd seen had been her seatmate's notes, scrawled in a script she didn't recognize. Maybe it was code, or a foreign language such as Arabic, possibly the details of a plot to destroy innocent lives aboard Flight 3950. She may have felt it her duty to alert the authorities. The curly-haired man was, the agent informed him politely, suspected of terrorism.

The curly-haired man laughed.

He laughed because those scribbles weren't a foreign language or some special secret terrorist code. They were math.

Yes, math. A differential equation, to be exact.

Had the crew quickly Googled this good-natured, bespectacled passenger, they might have learned that he — Guido Menzio — is a University of Pennsylvania economist known for his work on search theory.

They might also have discovered that last year he was awarded the prestigious Carlo Alberto Medal, given to the best Italian economist under 40. That's right: He's Italian, not Middle Eastern, or whatever heritage ordinarily gets ethnically profiled on flights these days.

Menzio was on the first leg of a connecting flight to Ontario, where he would give a talk at Queen's University. His nosy neighbor had spied him working out some properties of a price-setting model. Perhaps she couldn't differentiate between differential equations and Arabic.

Menzio showed the authorities his calculations and was allowed to return to his seat, he told me by email. He said the pilot seemed embarrassed. Soon, the flight took off, more than two hours late.

The woman never reboarded.

A spokesman for American Airlines said the woman had indeed initially told the crew she was sick, but when she deplaned she said the reason for her illness was the troubling behavior of her seatmate. At that time, she requested to be rebooked on another flight. The crew then called for security personnel, who interviewed Menzio and determined him not to be a "credible threat." (The spokesman could not disclose the female passenger's name for privacy reasons, so I wasn't able to contact her for comment.)

Menzio says he was "treated respectfully throughout," but remains frustrated by a "broken system that does not collect information efficiently." He's troubled by the ignorance of his fellow passenger, as well as "a security protocol that is too rigid — in the sense that once the whistle is blown everything stops without checks — and relies on the input of people who may be completely clueless."

Rising xenophobia stoked by the presidential campaign, he suggested, may soon make things worse for people who happen to look a little other-ish.

"What might prevent an epidemic of paranoia? It is hard not to recognize in this incident, the ethos of [Donald] Trump's voting base," he wrote.

In this true parable of 2016 I see another worrisome lesson, albeit one also possibly relevant to Trump's appeal: That in America today, the only thing more terrifying than foreigners is ... math.

Twitter, @crampell