Two science questions are answered: (1) How can someone have one brown eye and one blue eye?, and (2) Why are magnets attracted to some metals, but not all metals? It is very rare that a human will have two irises of different colors. This condition, heterochromia, can be a normal variant or the result of an ocular disease. Heterochromia can result from trauma before or shortly after birth, faulty development of eye pigmentation, and genetic conditions such as Waardenburg's syndrome and Horner's syndrome. Also, a section of one iris may be a different color than the rest of the iris. Physical trauma from an injury (unrelated to birth, as mentioned above) can also lead to changes in the appearance of eye color. On the other hand, while most atoms are intrinsically magnetic, most solids are not. Atomic magnetism arises principally from its electrons, which are themselves invariably magnetic. However, when the atoms assemble into solids, most of this atomic magnetism is lost due to cancellation. Only a few solids, including iron, nickel, and cobalt, retain some of their atomic magnetism. In these special solids, known as ferromagnets, many of their magnetic electrons align with one another to produce strong magnetic characteristics. Because of this internal magnetism, ferromagnetic solids experience the pull of a nearby magnet.