Castor is a plant that produces seeds (beans). Castor oil is produced from ripe seeds that have had their outer covering (hull) removed. Castor oil has been used as a medicine for centuries.
Castor oil is used for constipation and bowel preparation prior to colonoscopy, Childbirth, and many other conditions. The hull of the castor seed contains a deadly poison called ricin. This is why the hull must be removed before use. Ricin has been tested as a chemical warfare agent. Weapons-grade ricin is purified and produced in particles that are so small they can b breathed in.