The protein ricin (pronounced rye-sin) is a poison manufactured from the castor bean (Ricinus communis). Its name comes from the seed's resemblance to the tick. Ricin can be extracted from castor beans and is known to have an average lethal dose of 0.2 milligrams (1/5,000th of a gram), though some sources give higher figures. It is considered to be twice as deadly as cobra venom.