A package intended for a United States Senator has tested positive for ricin at a US Post Office sorting facility.

Ricin is a natural poison made from the castor oil plant. Just a few grains of ricin powder is enough to kill a human being.

The ricin was contained in an envelop sent to Mississippi senator Roger Wicker. There have been about twenty reported instances of ricin incidents in the last 30 years.

This video describes the plant that makes ricin.