Castor is a plant that produces seeds (beans). Castor oil is produced by pressing ripe seeds that have had their outer covering (hull) removed. The hull contains a deadly poison called ricin. Castor oil has been used as medicine for centuries.Castor bean plants are beautiful. They have vibrant red leaves and they produce red and yellow flowers. They're also extremely toxic to both people and animals. Like red kidney beans castor beans contain high concentrations of a particularly harmful lectin. The lectin in castor beans is called ricin.