Paraskevidekatriaphobia – that’s a word you don’t see every day of the week – means the fear of Friday the 13th. Despite its fearsome scientific name, the superstition that this day is unlucky is surprisingly common, even in societies which consider themselves well-educated and modern. When I was wondering what to write about this month, I happened to notice that it was Friday the 13th of October, so I thought that might make an interesting subject.