Sequence of castor bean (Ricinus communis) seed germinating. The seeds are extremely toxic. This plant is a source for ricin, a toxin poisonous to animals and insects as well as humans. It is a potent cytotoxin; as little as one milligram can kill an adult. Ricin inhibits protein synthesis and can lead to death within a few days. Both the plant and beans (seeds) should be kept away from children. The castor bean is the source of castor oil and is commonly grown in home gardens for its decorative leaves.