(CNN) -- A Texas actress who pleaded guilty to sending ricin-laced letters to President Barack Obama and then-New York City Mayor Michael Bloomberg has been sentenced to 18 years in federal prison, prosecutors say.
Here's a look at what you need to know about ricin, a natural, highly toxic compound that is extracted from castor beans.
Facts: About one million tons of castor beans are processed every year. Ricin is part of the waste from the beans when castor oil is made. Sometimes this is called "mash."
Less than a pinpoint can kill a human if ingested, injected, or inhaled. There is no known cure.
Ricin can be used in powder, pellet, mist or acid form.
Ricin can be produced easily and cheaply but analysts say as a weapon it is most effective on individuals.
If injected, ricin causes immediate death of the muscles and lymph nodes near the site of the injection. Failure of the major organs and death usually follow.
If ingested it causes nausea, vomiting and internal bleeding of the stomach and intestines, followed by failure of the liver, spleen and kidneys, and death by collapse of the circulatory system.
If a castor bean is swallowed whole without damage to the seed coat, it will probably pass harmlessly through the system. But if the coat is chewed or broken, then swallowed, the poison will enter the body.
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