All kinds of animals seem to have a magnetic sense. But what kind of organ can sense like magnetism? Nobody knows. One idea is that there would be particles of this magnetic mineral called magnetite dotted all over the body of the animal, or they may be concentrated in a small area. As the animal moves within the Earth's magnetic field, the magnetite granules are subject to mechanical stresses produced by their movement in the field. Those stresses are linked to the central nervous system of the organism and enable it somehow to interpret the direction it's headed in. So that's probably that mechanism that is used by some of these animals that navigate magnetically.