You doubtless all remember the way Holmes would cast an eye over some total stranger and say: ah, obviously a captain in the Merchant Navy recently returned from Valparaiso, and, I note, a Freemason. And you, Madam, are a typewriter. Etcetera. I suddenly noticed that I have quite an extensive callus at the base of my first finger (right hand only); the only one I possess. Not even with respect to myself can I do the Sherlock trick. I cannot think why I’ve got it. I do almost nothing except type and, to a limited extent, write with a pen. I am surprised sometimes that the ends of my fingers are not like little hooves, but in fact, the computer seems to have left no particular trace. Writing with a pen has caused slight, barely perceptible, thickening of the skin on the inner surface of my third finger. And the callus? There must be an explanation, but I’m blest if I can think of it. I must be losing my marbles.