It's not the first time the toxin has made headlines. In 1978, Georgi Markov, a Bulgarian dissident, was assassinated in London when a man approached and jabbed him with an umbrella modified to fire a ricin pellet.

Ricin is a naturally occurring toxin that comes from the castor bean, Ricinus communis, an ornamental plant introduced from India. According to Casarett and Doull's Toxicology: The Basic Science of Poisons, the fatal dose for a child can be five to six seeds. For an adult, it is 20, however because the toxin protein is largely destroyed by the intestine, the mortality rate from swallowing the beans is low—less than 10 per cent.

What about ricin that has been modified into a powder