1. What is Novichok?

The word — pronounced novee-CHOCK — means “the new guy” in Russian, which is no coincidence. It refers to the fourth generation of solid nerve agents developed in the former Soviet Union, ones manufactured from materials that remain legal under the international Chemical Weapons Convention that took effect in 1997. These co-called binary agents (meaning they become lethal only when combined) were first made as ultrafine powders but can be turned into liquids and gas. The toxins belong to a chemical family called organophosphates, and because they’re related to pesticides (which are also known to have nervous-system effects), their development was sometimes cloaked as an agricultural effort.

2. How does it work and what does it do?

Former Russian spy Sergei Skripal in March was found foaming at the mouth, struggling to breathe and making strange movements with his hands; the eyes of his adult daughter, Yulia, were described as wide open but completely white. Charles Rowley and his girlfriend, Dawn Sturgess, collapsed hours apart on Saturday at a house in Amesbury, displaying symptom that police initially mistook as pointing to contaminated heroin or crack cocaine. Agents like Novichok can enter the body by being eaten or inhaled, or through the skin, and block the action of cholinesterase, an enzyme that breaks down a nervous-system protein called acetylcholine. The resulting buildup interferes with the brain’s communication with muscles and glands throughout the body, resulting in what the U.S. Centers for Disease Control and Prevention calls “cholinergic syndrome”: uncontrolled secretions in the lungs and mouth, diarrhea and vomiting, sweating, convulsions, delusions, racing heartbeat and generalized weakness that can progress to paralysis, suffocation and death. Children are particularly vulnerable to the poison, because they have less capacity than adults to eliminate toxins.

3. What’s the risk to the public?

That would depend on the form in which Novichok is administered, which at the moment isn’t clear. The new victims were found in a house eight miles from Salisbury, where the March poisoning occurred. If delivered as a fine powder that clings to clothing, such “dusty” nerve agents can be spread widely. Traces of Novichok were found in a restaurant and a bar near where Skripal and his daughter were found, but the area was thoroughly decontaminated. Even so, the couple that fell ill Saturday were in Salisbury a day earlier, near roads that had been sealed off during the Skripal investigation, according to the Independent. Counterterrorism police are investigating a possible connection between the two incidents.

4. What could doctors do?

Poisoning with organophosphates can be treated with atropine, a drug that blocks acetylcholine, although it isn’t an antidote. Vil Mirzayanov, a former Russian chemist at Russia’s State Research Institute of Organic Chemistry and Technology, told Sky News that those who were exposed could be at risk of illness for years to come. He said slight exposure could produce headaches, cognitive difficulty and problems with coordination.

5. Why does this point to Russia?

The agents that make Novichok were secretly developed by the former Soviet Union during the later years of the Cold War. Mirzayanov spent years testing and enhancing them before exposing the program in 1991; he was charged with treason and now lives in exile in the U.S. He says only the Kremlin knows how to make Novichok and he doubts a nonstate actor could have weaponized it. There’s also the choice of target — Skripal sold the identities of Russian agents to Britain’s MI6, and was released by Russia in a 2010 swap of ex-spies — as well as the weight of history: A U.K. inquiry said Russians were almost certainly behind the 2006 poisoning in London, with polonium, of Alexander Litvinenko, another ex-spy. Russia rejects the suggestion.

Prime Minister Theresa May in March accused Russia of being behind the Skripal poisonings and expelled 23 diplomats in retaliation. She also pledged that government officials and the royal family would boycott the World Cup soccer tournament, hosted by Russia. Russia has denied involvement.

6. What can the world do about Novichok?

Not much, perhaps. Russia, like most nations of the world, is a signatory to the Chemical Weapons Convention, which requires members to destroy any such weapons and the facilities that produced them. (Only Egypt, North Korea and South Sudan haven’t signed the accord; Israel signed but hasn’t ratified.) And Russia said last year that it had destroyed all its stocks of banned chemical weapons. The pact is overseen by the Organization for the Prohibition of Chemical Weapons, based in The Hague. Peter Wilson, the U.K.’s representative to the group, said on March 13 that Russia “has failed, for many years, to declare chemical weapons development programs dating from the 1970s.” Russia is not the only problem. The European Union and the U.S. have imposed sanctions on people and companies to try to stop the transfer of materials and substances that may have been used by President Bashar al-Assad’s regime in Syria to manufacture chemical weapons.