Why "Cow" magnet? Farmers often place one of these cow magnets in the cow's stomach to attract nails or small pieces of iron that the cow ingests. This prevents damage to a cow's stomach or 'Hardware Disease.'This standard Alnico cow magnet has a magnetic pole on each end, and is perfect for a 3-D demonstration of magnetic fields, similar to that produced by the earth. Simply put the cow magnet into a test tube, then lower the test tube into a clear 16-oz. soda bottle filled with mineral oil (or glycerin) and iron filings. Shake the bottle. The iron filings will line up all the way around the cow magnet to show its magnetic field in 3-D! The cow magnet is stronger than typical bar magnets of equal size.