Ricin is a poison that is naturally found in castor beans, produced by the pervasive castor bean weed. It can be formed into a powder, mist or pellet, or even added to water, according to the federal Centers for Disease Control and Prevention.
Castor beans are processed throughout the world to make castor oil. Ricin is the part of the waste "mash" produced when castor oil is made.
This concentrated ricin kills people by attacking their cells. It gets absorbed into individual cells, and then starts preventing the cells from making the proteins they need to survive. The cells die, and ultimately the body's systems fail, which can lead to death.
The symptoms of ricin poisoning might not raise an alarm until it's too late. They begin benignly enough -- respiratory distress, followed by nausea, coughing, fever and, ultimately perhaps, death.
Ricin-associated illness cannot be spread from person to person through casual contact. However, if you come into contact with someone who has ricin on their body or clothes, you could become exposed to it.
There is no antidote for ricin poisoning. If you are exposed, you will need to get the ricin off of your body as quickly as possible. Poisoning is treated by medical care to minimize the effects.
The U.S. military is said to have experimented with using ricin as a possible warfare agent, and ricin was possibly used in the 1980s in Iraq. Some terrorist organizations have also tried to harness its power, according to the CDC.
But the single most infamous ricin incident occurred in 1978 and has been dubbed "the umbrella murder."
Georgi Markov, a Bulgarian dissident writer and journalist who was living in London at the time, was assassinated by a man who used a rigged umbrella to fire a poisonous ricin pellet into his leg. Markov became ill and died several days later.
Although Markov's death-by-ricin poisoning remains unsolved -- making it one of the most enduring mysteries of the Cold War -- it's speculated that the Bulgarian secret police and the Soviet KGB were behind Markov's death.