The anti-government protests in Iran appear to have died down this week, but they could erupt again at any moment.

They also offer a helpful reminder: Food is the ultimate weapon.

When Iranians took to the streets at the end of December, they voiced their objections to everything from government corruption and repression to the military adventurism that has provided money and resources to foreign soldiers and terrorists.

But the unrest that captured the world’s attention may have boiled down to something as simple as the rising price of eggs.

“Eggs used to be 100,000 rials,” said one Iranian man, referring to Iran’s currency, in his effort to explain the strife. “Now they are 210,000.” In U.S. dollars, this means that their cost jumped from about $2.77 to $5.82.

The source for this quote is a British newspaper, the Telegraph, which several days ago spoke to “Majid Ahadi,” the pseudonym of an Iranian who needed to protect his true identity from the government’s security forces.

That’s how bad things are in Iran: People can’t even complain about food inflation, which has affected much more than just eggs, without fearing for their personal safety. Since the protests broke out on December 28, government forces have killed more than 20 people and arrested hundreds.

President Trump sounded off in a tweet on New Year’s Day: “The great Iranian people have been repressed for many years. They are hungry for food & freedom. Along with human rights, the wealth of Iran is being looted. TIME FOR CHANGE!” The next day, he tweeted again about Iran: “The people have little food, big inflation and no human rights.”

I’ve always said that when people are hungry, they’ll do desperate things—and when their children are starving, they’ll do anything.

That’s why the rising cost of food can lead to political instability, even threatening to topple entrenched rulers in despotic countries.

Feeling a sense of déjà vu? Seven years ago, the Arab Spring demonstrations jolted the Islamic world—and they started over food as well.

In Tunisia, officials confiscated the fruits and vegetables of Mohamed Bouazizi, a street vendor who operated a food cart, apparently because he refused to pay a bribe. His response was extreme: He committed suicide by lighting himself on fire.

It might have seemed like a futile gesture, but in Tunisia, the president was forced from office—and in North Africa and around the Middle East, protestors took to the streets.

Western optimists had hoped that the Arab Spring would inaugurate an era of political freedom and religious tolerance. Unfortunately, this was not to be: If anything, the region appears even more chaotic today, with ISIS only recently defeated, Syria in shambles, and Saudi Arabia and Iran conducting a proxy war in Yemen and around the Persian Gulf.

It’s too soon to know what the turmoil of the last two weeks will mean for Iran, whose problems go well beyond food prices. The government in Tehran claims that the unemployment rate is about 12 percent, but the Associated Press reports that it’s really about two-and-a-half times as high. The Economist adds that the average Iranian is about 15 percent poorer today than he was about a decade ago.

Sanctions can explain only so much of this misery. For years, they suffocated Iran’s economy, but since their lifting after the nuclear deal in 2015, ordinary Iranians still haven’t enjoyed much of a dividend—in part because Iran’s government has focused on other priorities.

Last month, a United Nations report provided compelling evidence that Iran has exported missiles, drones, and other equipment to rebels in Yemen. Around the same time, the regime announced a new budget that boosts subsidies for radical religious organizations and increases military spending while also cutting welfare programs.

The irony is that while Iran’s rulers have sent sophisticated weapons abroad and at home have pursued a nuclear program that could lead to the development of the most powerful weapon in the world, they may have forgotten a simple truth that its own people understand: The ultimate weapon is food.