I watched a video recently where he took a piece of cereal, put it in water, and then started moving it around with a magnet. Most people would say it's because there is Iron in the cereal which is attracted by the magnet. But then they started messing around with objects that weren't magnetic like plastic and paper, the results?.... They moved as well! The physics behind this is that water is Diamagnetic which means that when in the presence of a magnetic field, it creates it'sown opposite magnetic field. This means that the water is repelled slightly causing a depression which causes those objects to move in the water.