Castor oil is a thick, pale yellow liquid pressed from the seeds of the castor plant. For centuries, parents gave their children spoonfuls of castor oil as medicine, believing it cured everything from stomachaches to colds. The oil tastes terrible (imagine licking a candle), so kids dreaded it. In old books and movies, you'll often see children trying desperately to avoid taking their castor oil while adults insist “it's good for you.”

Today we know castor oil works mainly as a powerful laxative, meaning it helps people who are constipated. Doctors rarely recommend it anymore because gentler medicines exist. However, castor oil still has many uses outside medicine. Manufacturers add it to soaps, paints, plastics, and even biodiesel fuel. Mechanics use it as a lubricant for engines and machinery because it stays slippery even at high temperatures.

The castor plant grows wild in warm climates, but its seeds are poisonous if eaten whole. The oil-making process removes the poison, leaving only the useful oil behind. Despite its awful taste and old-fashioned reputation, castor oil remains surprisingly useful in the modern world.