The use of Russian-developed nerve agent Novichok to poison ex-spy Sergei Skripal and his daughter makes it "highly likely" that Russia was involved in the incident, according to the British government.
Novichok refers to a class of nerve agents developed in the Soviet Union near the end of the Cold War, ostensibly created to avoid a recently signed international chemical weapons treaty which did not cover new chemical agents.
Novichok behaves slightly differently than other nerve agents, with some reports that the class of substances is deadlier than similar chemicals like sarin or VX and harder to identify. Nerve agents are typically inhaled or absorbed through the skin.
Normally nerve cells control muscle activity using neurotransmitters, or chemical messengers.
When they make contact with receptors on the muscle cell, the muscle contracts.
An enzyme is then released to help disable the neurotransmitter and allow the muscle to relax.
Poisons like nerve agents hijack this process, blocking the enzyme which allows the muscle to relax.
This means muscles like the heart and others which control breathing become paralyzed, leading to seizures and potentially death.