Counterterrorism police in the UK have today confirmed that a former Russian spy who worked for the British Intelligence Agency MI6, Sergei Skripal, and his daughter Yulia, fell into a critically ill condition this week after deliberate "exposure to a nerve agent".
The police officer who first attended the scene is also seriously ill in hospital. All of them are suffering from exposure to the nerve agent, which the police have now identified.
Nerve agents have been described as the most dangerous thing humans have ever made, other than the atom bomb. So what are they, exactly?
What are nerve agents and what do they do to your body?
Nerve agents are highly poisonous chemicals that prevent the nervous system from functioning properly. There are several different types, including Sarin, Tabun, VX, and Soman.
They all work in a similar way, overstimulating your nervous system, causing your muscles to contract uncontrollably.
VX, short for venomous agent X, makes you unable to breathe within a matter of seconds or minutes, depending on the dose and whether it was ingested or administered through skin contact.
Early symptoms of VX poisoning include vomiting, shortness of breath and a runny nose. However, the toxin acts so quickly that there is rarely time for treatment before death.
Sarin, mainly administered as a gas, also causes respiratory failure, convulsions, loss of consciousness, diarrhea, paralysis, excessive drooling, and sweating, according to the Centers for Biological Diversity (CDC).
White eyes (due to constriction of the pupils) is also common in victims of poisoning.