NOVICHOK is a highly toxic nerve agent that is so powerful even a pinprick can kill in minutes.
The odourless and clear toxin was developed in Russia and is behind the attempted murders of ex-Soviet double agent Sergei Skripal, his daughter Yulia, and the poisoning of a couple in Amesbury, Wilts.
How does Novichok kill?
Novichok is designed to be among the deadliest nerve agents ever created.
Russian scientists who developed it between 1971 and 1993 claim that some variants are up to eight times more potent than the highly toxic VX.
Novichok can be ingested through the skin and disrupts the transmission of chemicals through the body's nervous system.
One substance, acetylcholine, builds up in the nerves, causing muscles to contract and spasm uncontrollably.
Breathing soon becomes impossible as the diaphragm stops working and the victim goes into cardiac arrest as the muscles in the heart fail.
What does Novichok do to the human body?
Novichok agents, dispersed as an ultra-fine powder rather than vapour, belong to the class of inhibitors called "organophosphate acetylcholinesterase".
They prevent the normal breakdown of a neurotransmitter acetylcholine which, when it builds up, causes muscles to contract involuntarily.
Because the victim's heart and diaphragm aren't functioning properly, this leads to respiratory and cardiac arrest.
Those affected usually die from total heart failure or suffocation as copious fluid secretions fill their lungs.
But even if they don't die, the substance can also cause permanent nerve damage, leaving victims permanently disabled, Russian scientists have said.
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What are the symptoms of Novichok poisoning?
Symptoms include intense breathlessness, muscle pain, vomiting and loss of consciousness.
Novichok agents may cause lasting nerve damage, resulting in permanent disablement of victims.
Andrei Zheleznyakov, one of the scientists involved in their development, was accidentally exposed to Novichok in a Moscow lab in 1987.
He was critically injured and took ten days to recover consciousness after the incident.
He lost the ability to walk and was treated at a secret clinic in Leningrad for three months afterwards.
The agent caused permanent harm, with effects that included "chronic weakness in his arms, a toxic hepatitis that gave rise to cirrhosis of the liver, epilepsy, spells of severe depression, and an inability to read or concentrate.
He eventually died just five years later.