Not many people put a whole lot of thought into what their morning cereal is made of. Most people would just assume there's some grain and maybe a little sugar, or a lot of sugar if you're more of a Lucky Charms person than a Raisin Bran person. Nobody would suspect, though, that there would be metal in their Cheerios. Turns out, Cheerios are magnetic. Or are they?
Fill a bowl with water and drop in a couple Cheerios. Take a magnet and hold it just above the Cheerios, the Cheerio will be attracted toward the direction of the magnet. Why is this? If the little cereal ring is magnetic, then there must be metal fragments in it causing the attraction. Now the cereal is all magnetic, and it does contain tiny fragment of iron. This is perfectly reasonable though, as iron is a key nutrient in a human diet. But that's not the whole story,
If you were to try this with objects other than cereal, say a small piece of paper or plastic, it would still seem to be attracted to the magnet as it floated in the water. The "attraction" you see is actually all about water, which is diamagnetic, meaning it generates a magnetic field opposite to that of the magnetic field it is in the presence of. Thus, the water is slightly repelled by the magnet. This causes a slight divot in the water, that the object in the bowl actually falls into, making it appear to follow the magnet. In actuality, it isn't being affected directly by the magnetic field, but by the waters reaction to the magnetic field.