chrb pointed out a story at BBC News about the discovery of a light-sensitive protein in the human eye that acts like a "compass" in a magnetic field
. The molecule at the center of the study is called cryptochrome and is found in every animal on Earth. If removed from the eyes of flies, the flies lost the ability to respond to a magnetic field. From the article: "Despite much controversy, no conclusive evidence exists that humans can sense the Earth's magnetic field, and the find may revive interest in the idea. Although humans, like migratory birds, are known to have cryptochrome in their eyes, the idea of human magnetoreception has remained largely unexplored since pioneering experiments by Robin Baker of the University of Manchester in the 1980s."