Vladimir Kara-Murza presents a 2014 report in Washington, D.C., on corruption at Russia’s Sochi Olympics. PHOTOGRAPH BY ALEX WONG/GETTY

Last Saturday, on a beautiful, sunny afternoon, a friend and I were in Moscow discussing precautions. I confessed to a fear of apartment-building entryways because two people I knew, the parliament member Galina Starovoitova and the journalist Anna Politkovskaya, had been shot dead on their way up to their apartments. “Ever since Nemtsov was killed,” my friend said, referring to the February shooting of a Putin opponent, “I don't know anything about precautions anymore. What are you supposed not to do now—walk the streets?”

It would also be prudent now to stop eating and drinking. On Wednesday, Vladimir Kara-Murza, a thirty-three-year-old opposition journalist, was hospitalized in critical condition after he collapsed at his office in Moscow. He was diagnosed with renal failure that had resulted from acute intoxication. Put more simply, some sort of poison was causing Kara-Murza's illness.

His father, recounting his conversations with Kara-Murza's doctors, has stressed that they do not know exactly what caused the intoxication, but Kara-Murza's wife and others have said that they suspect foul play. Assuming foul play, it is not clear when and how Kara-Murza may have been poisoned.*** **Russian activists and journalists who get enough death threats and take them sufficiently seriously to hire bodyguards are also usually careful about what they ingest. Soon after the chess champion Garry Kasparov quit the sport to go into politics full time, in 2004, he hired a team of eight bodyguards, who not only accompanied him everywhere but also carried drinking water and food for Kasparov to eat at meals shared in public. Three years ago, Kasparov told me that what he liked most about foreign travel was being able to shed his bodyguards for a while. A year after that, threats drove him to leave Russia permanently.

Attacks by poisoning are possibly even more common in Russia than assassinations by gunfire. Most famously, Alexander Litvinenko, a secret-police whistle-blower, was killed by polonium in London, in 2006. Last week, British newspapers reported that a Russian businessman who dropped dead while jogging in a London suburb in 2012 had been killed by a rare plant poison. He had been a key witness in a money-laundering case that had originally been exposed by the Moscow accountant Sergei Magnitsky, who was tortured to death, in 2009, in a Russian jail.

Two years before Politkovskaya was shot, she suffered multiple-organ failure after ingesting a poison, still unidentified, with tea served to her on a Russian plane. Yuri Shchekochikhin, her colleague at the investigative weekly Novaya Gazeta, died in a Moscow hospital, in 2003, as the result of an apparent poisoning. In 2008, a lawyer who specializes in bringing Russian cases to the European Court of Human Rights, Karinna Moskalenko, fell ill in Strasbourg; her husband and two small children were also unwell. The cause of their illness was identified as mercury that had somehow found its way into their car.

Moskalenko was one of the lead lawyers in the defense of Mikhail Khodorkovsky, an oil tycoon who had become Putin’s most famous political prisoner. He spent ten years behind bars before Putin granted him clemency before the Sochi Olympics; he is now living in Zurich and running an anti-Putin N.G.O., Open Russia, with offices in London, Prague, and Moscow. Last month, the Moscow office was raided by law enforcement, which seized many of the computers. (Some have since been returned.) Kara-Murza runs Open Russia’s multi-city public-lecture program—a difficult job, because most cities in Russia try to shut down his events. The organization itself has so far escaped being shut down because, on paper, it doesn’t exist: using a loophole in the law, it has simply not registered—and hence cannot be liquidated the way many other Russian N.G.O.s have been in the past three years.

Like the Soviet regime before it, the Putin government spreads fear by destroying the illusion that one can protect oneself. So Open Russia’s leaders think that they can use a loophole in the law to keep themselves safe? the message seems to be. Let’s see how safe they feel after one of them is poisoned.

Indeed, the larger message of the Nemtsov assassination and the apparent attempted assassination of Kara-Murza is that no one is safe. Both men are sufficiently well-known to attract the attention of Russia’s dwindling oppositional minority, but neither has the superstar status that would preclude identifying with him. If Litvinenko’s murder made one think, “Well, but who’d be interested in me?,” these attacks put many more people on notice. Don’t walk the streets. Don’t eat the food. Don’t talk.

Speaking of talking, in the past few months, people who work at two Moscow restaurants have warned me, separately, about the precise locations of listening devices at the eateries. The warnings came unbidden. The food at both places was, incidentally, not only very good but also apparently safe. That, along with the springtime sun, helps maintain the bizarre sense of normalcy that has a way of going hand in hand with the mortal danger that has become a fact of everyday life.

* This post has been updated to reflect comments from Kara-Murza's doctors about the nature of his illness.