Ricin is indeed a potent poison, but I'm not sure about its oral efficacy.
It was used spectacularly by the Bulgarian secret service to poison Georgi Markov, a dissident who worked for the BBC World Service.
Markov was crossing one of the Thames bridges when he felt a sharp sting on the back of his leg. He turned and thought he had been accidentally poked by an umbrella, and then carried on.
He thought little more of it, but when he got home after telling his wife of his day he later collapsed, sweating profusely, fell into a coma and died before morning.
Doctors were baffled. The pathologist who carried out the PM spotted a small black mark on the back of Markov's leg, and almost dismissed it as a boil or spot, but a hung made him look forther.
Just under the skin was an irridium sphere, just a few microns across, with a hole running through it. In the hold were microgrammes of ricin.
The inquest concluded that Markov had been murdered, and the the sting in his leg on the bridge earlier that day had been the ricin pellet, shot from an airgun disguised as an umbrella.
The pellet is still in the black museum at New Scotland Yard, along with many other strange and macabre curios.