Honestly - academics! Just read the lovely (and delightfully short) La Dame Aux Camelias by Alexandre Dumas which is about a youthful love affair. I hadn't finished my train journey so I read the foreword.
The (male) professor who wrote the foreword states that the love interest was based on Marie DuPlessis, a courtesan. Apparently she carried white camelias when in her box at the opera, except for 5 days a month, when she carried red camelias, and according to him, no-one knows why.
Erm... can anyone think of why a courtesan might carry red camelias 5 days a month?!
Anyone?!