So, while reading the Christie I mentioned in my previous post, I came across two little bits of information that were new to me
First, in "The Kidnapped Prime Minister", one of the two members of the War Cabinet who come to engage Poirot is described as 'Leader of the House of Commons'. That puzzled me, since I'd always thought the leader of the House of Commons was the Prime Minister. Turns out (thank you, Wikipedia) this is sometimes the case and sometimes not: in recent years, that job has usually been handed off to one of the other major figures in the cabinet. Live and learn.
The other was a different version of a well-known superstition. At one point in "The Adventure of the Cheap Flat" Poirot observes "It is still regarded as a symbol of good luck if a black cat crosses your path". This was surprising, since I've always heard it the other way round: that it's bad luck when a black cat crosses your path -- which, since I love black cats, I've always considered stuff and nonsense; for me getting to see a new cat is cause for celebration. I wonder if this reversal is a US/UK thing, since I was once surprised, when a bird dropped its business on me when I was out walking with an English friend, to have him say "lucky you". At first I thought he was kidding, but he stuck to his guns, insisting that having a bird poo on you is good luck.
It's sometimes said the English and Americans are one people divided by a common language, but I wonder if it doesn't go a little deeper than that, into unshared superstitions as well.
current reading: THE SHADOW (The Mother Goose Murders/Crime Over Casco) 
16 hours ago