Have you ever emerged from a matinee movie, squinted into the sudden burst of sunlight and sneezed uncontrollably? Up to a third of the population will answer this question with an emphatic "Yes!" (whereas nearly everyone else scratches their head in confusion). Sneezing as the result of being exposed to a bright light—known as the photic sneeze reflex—is a genetic quirk that is still unexplained by science, even though it has intrigued some of history's greatest minds.

Aristotle mused about why one sneezes more after looking at the sun in The Book of Problems: "Why does the heat of the sun provoke sneezing?" He surmised that the heat of the sun on the nose was probably responsible.

Bacon's best guess was that the sun's light made the eyes water, and then that moisture ("braine humour," literally) seeped into and irritated the nose.

So neurology steps in: Most experts now agree that crossed wires in the brain are probably responsible for the photic sneeze reflex.