Today's useless fact - What is 'deja vu' exactly, and what explanations are out there that account for why people experience it?

The deja-vu (French "already seen") phenomenon is just that: a strange but by no means rare occurrence in which a person has a sensation of having been in a particular situation before. The English poet Tennyson expressed the idea beautifully in 'Locksley Hall' when he spoke of a feeling that reminded him 'of something done, of something shared, of something said, I know not where, such as no mortal can declare' (or words to that effect.) Informed explanations vary, ranging from the supernatural to denial. One popular theory explains deja-vu by the fact that in some situations our brains process information so rapidly that we get the feeling we have been through or in this situation before, when in fact, what we heard or saw or experienced happened just nano-seconds before. Check out the links in our Deja Vu category for more.