Marina Dubrova, an English teacher on the Russian island of Sakhalin in the Pacific, showed an uplifting YouTube video to her eighth-grade class last month in which children, in Russian and Ukrainian, sing about a "world without war".
After she played it, a group of girls stayed behind during recessand quizzed her on her views.
"Ukraine is a separate country, a separate one," Dubrova, 57, told them.
"No longer," one of the girls shot back.
A few days later, the police came to her school in the port town of Korsakov. In court, she heard a recording of that conversation, apparently made by one of the students. The judge handed down a US$400 fine for "publicly discrediting" Russia's Armed Forces. The school fired her, she said, for "amoral behaviour".
"It's as though they've all plunged into some kind of madness," Dubrova said in a phone interview, reflecting on the pro-war mood around her.
With President Vladimir Putin's direct encouragement, Russians who support the war against Ukraine are starting to turn on the enemy within.
The episodes are not yet a mass phenomenon, but they illustrate the building paranoia and polarisation in Russian society. Citizens are denouncing one another in an eerie echo of Josef Stalin's terror, spurred on by vicious official rhetoric from the state and enabled by far-reaching new laws that criminalise dissent.
There are reports of students turning in teachers and people telling on their neighbours and even the diners at the next table. In a mall in western Moscow, it was the "no to war" text displayed in a computer repair store and reported by a passerby that got the store's owner, Marat Grachev, detained by the police.
In St. Petersburg, a local news outlet documented the furore over suspected pro-Western sympathies at the public library; it erupted after a library official mistook the image of a Soviet scholar on a poster for that of Mark Twain.
In the western region of Kaliningrad, authorities sent residents text messages urging them to provide phone numbers and email addresses of "provocateurs" in connection with the "special operation" in Ukraine, Russian newspapers reported; they can do so conveniently through a specialised account in the Telegram messaging app. A nationalist political party launched a website urging Russians to report "pests" in the elite.
"I am absolutely sure that a cleansing will begin," Dmitri Kuznetsov, the member of Parliament behind the website, said in an interview, predicting that the process would accelerate after the "active phase" of the war ended. He then clarified: "We don't want anyone to be shot, and we don't even want people to go to prison."
But it is the history of mass execution and political imprisonment in the Soviet era and the denunciation of fellow citizens encouraged by the state that now loom over Russia's deepening climate of repression.
Putin set the tone in a speech March 16, declaring that Russian society needed a "self-purification" in which people would "distinguish true patriots from scum and traitors and simply spit them out like a fly that accidentally flew into their mouths."
In the Soviet logic, those who choose not to report their fellow citizens could be viewed as being suspect themselves.
"In these conditions, fear is settling into people again," said Nikita Petrov, a leading scholar of the Soviet secret police. "And that fear dictates that you report."
In March, Putin signed a law that punishes public statements contradicting the government line on what the Kremlin terms its "special military operation" in Ukraine with as much as 15 years in prison. It was a harsh but necessary measure, the Kremlin said, given the West's "information war" against Russia.
Prosecutors have already used the law against more than 400 people, according to the OVD-Info rights group, including a man who held up a piece of paper with eight asterisks on it. "No to war" in Russian has eight letters.
"This is some kind of enormous joke that we, to our misfortune, are living in," Aleksandra Bayeva, the head of OVD-Info's legal department, said of the absurdity of some of the war-related prosecutions. She said she had seen a sharp rise in the frequency of people reporting on their fellow citizens.
"Repressions are not just done by the hands of the state authorities," she said. "They are also done by the hands of regular citizens."
In most cases, the punishments related to war criticism have been limited to fines; for the more than 15,000 anti-war protesters arrested since the invasion began February 24, fines are the most common penalty, though some were sentenced to as many as 30 days in jail, Bayeva said. But some people are being threatened with longer prison terms.
In the western city of Penza, another English teacher, Irina Gen, arrived in class one day and found a giant "Z" scrawled on the chalkboard. The Russian government has been promoting the letter as a symbol of support for the war, after it was seen painted as an identifying marker on Russian military vehicles in Ukraine.
Gen told her students it looked like half a swastika.
Later, an eighth grader asked her why Russia was being banned from sports competitions in Europe.
"I think that's the right thing to do," Gen responded. "Until Russia starts behaving in a civilised manner, this will continue forever."
"But we don't know all the details," a girl said, referring to the war.
"That's right, you don't know anything at all," Gen, 45, said.
A recording of that exchange appeared on a popular account on Telegram that often posts inside information about criminal cases. The Federal Security Service, a successor agency to the KGB, called her in and warned her that her words blaming Russia for the bombing of a maternity hospital in Mariupol, Ukraine, last month were "100% a criminal case."
She is now being investigated for causing "grave consequences" under last month's censorship law, punishable by 10 to 15 years in prison.
Gen said she found little support among her students or from her school and quit her job this month. When she talked in class about her opposition to the war, she said she felt "hatred" toward her radiating from some of her students.
"My point of view did not resonate in the hearts and minds of basically anyone," she said in an interview.
But others who have been the targets of denunciation by fellow citizens drew more hopeful lessons from the experience. On Sakhalin Island, after local news outlets reported on Dubrova's case, one of her former students raised US$150 in a day for her, before Dubrova told her to stop and said she would pay the fine herself. On Friday, Dubrova handed the money over to a local dog shelter.
In Moscow, Grachev, the computer repair store owner, said he found it remarkable that not one of his hundreds of customers threatened to turn him in for the "no to war" text that he prominently displayed on a screen behind the counter for several weeks after the invasion. After all, he noted, he was forced to double the price of some services because of Western sanctions, surely angering some of his customers. Instead, many thanked him.
The man who apparently turned in Grachev was a passerby he refers to as a "grandpa" who, he said, twice warned his employees in late March that they were violating the law. Grachev, 35, said he believed the man was convinced he was doing his civic duty by reporting the store to the police and most likely did not have access to information beyond state propaganda.
Grachev was fined 100,000 roubles, more than US$,200. A Moscow politician wrote about the case on social media, including Grachev's bank details for anyone who wanted to help. Enough money to cover the fine arrived within two hours, Grachev said.
He received 250,000 roubles in total, he said, from about 250 separate donations, and he plans to donate the surplus to OVD-Info, which provided him with legal aid.
"In practice, we see that not everything is so bad," he said in an interview.
Grachev is now pondering how to replace his "no to war" sign. He is considering: "There was a sign here for which a 100,000 rouble fine was imposed."