Humour is a funny thing. Something which causes a seizure in one person will leave another inexplicably stony-faced. However, there is a small coterie for whom a certain type of humour resonates. Should you, in daylight, be passing Jarndyce Antiquarian Booksellers in Great Russell Street, Bloomsbury, you will often find two 9-year-old boys outside, cunningly disguised as a grey haired, middle-aged woman in sensible shoes (the author of this piece) and a balding, bespectacled gentleman (her solicitor). These two often attract the attention of bemused tourists on the way to the British Museum, as they scream with laughter at the titles of the books in the left-hand window of said shop.