"I did what little had to be done."

Lovers of classic murder mysteries will recognize the sentence in the title as a key element in Agatha Christie's The Murder of Roger Ackroyd.  For obvious reasons I'll defer any discussion of the plot, but there were several items of language and usage I thought might be worth mentioning.

"I don't know what Mrs. Cecil Ackroyd thought of the Ferrars affair when it came on the tapis."  Found the explanation on the Wikipedia disambiguation page:  "On the tapis, a Victorian phrase meaning 'on the table' or 'under consideration' (Tapis = tablecloth (Fr.)"

"I didn't think it would [do any good] either, but I protested in duty bound."  "Duty bound" is a familiar phrase, but the "in" seemed anomalous.  Found this: "Sources place this idiom's origin in the 1500s.  Digital records in the form in duty bound or by duty bound go back to at least the 1600s.  It appears as if the word in, however, started to disappear from use around the early 1900s."  

[describing Poirot]: "An egg-shaped head, partially covered with suspiciously black hair, two immense mustaches, and a pair of watchful eyes."  There is a lengthy discussion of this usage at Merriam Webster:

In other words: is mustache, linguistically speaking, properly singular or plural?... One thing that is notable about these early uses is that the plural is frequently used, even when the spelling is closer to the French moustache... Just as there was no consensus on spelling, there was no contemporaneous agreement about whether an individual possesses two mustaches or one. In another bilingual dictionary of the period, the Spanish word is presented as plural but the English word as singular... No less a writer than Shakespeare used the word in the singular (and note that excrement is here used in a now-obsolete sense meaning “outgrowth”):

"…for I must tell thee, it will please his grace, by the world, sometime to lean upon my poor shoulder, and with his royal finger thus dally with my excrement, with my mustachio..."

— William Shakespeare, Love’s Labour’s Lost, 1598

It may well be because of the example of whiskers that mustache was considered a plural for so long; they were, after all, synonymous terms.

More at the link, especially re the correct spelling of the term.  If I learn nothing else today, at least I know I can tell a mustachioed friend "Hey, I really like your excrement!"

"Flora joined me by the silver table, and expressed heretical doubts as to King Charles I ever having worn the baby shoe, "And anyway," continued MIss Flora, "all this making a fuss about things because some one wore or used them seems to me all nonsense.  They're not wearing or using them now.  The pen that George Eliot wrote The Mill on the Floss with - that sort of thing - well, it's only just a pen after all.  If you're really keen on George Eliot, why not get The Mill on the Floss in a cheap edition and read it?"  I'm storing this quote here for future use, because it is directly relevant to the most interesting thing I've read all year - but I don't have time to take a deep dive into that subject right now.

"Ralph's  nerves must have gone phut!  If he suddenly found out that his uncle had been murdered within a few minutes of his leaving him... well, he might get the wind up and clear right out."  I see this idiom all the time in mysteries - especially British ones.  The meaning is always clear - I know the person is alarmed or worried rather than having problems with flatus - but I never could parse the derivation of the phrase.  So today I looked it up and found a proper explanation at The Word Detective: 

“Put the wind up,” meaning “to alarm or make nervous,” as well as its close cousin “to get the wind up” (to become alarmed), both date to just after World War I, and are more often heard in the UK than in the US. The origin of the phrases apparently lies in the armed services slang of WWI (“Shells so close that they thoroughly put the wind up a Life Guardsman in the trench with me,” Wilfred Owen, 1918). But both phrases are still very popular, as can be seen in a recent headline from the UK-based technical website The Register, reporting on US alarm at the theft of a UK government computer containing various secrets: “MoD laptop thefts put the wind up the US.”

Evidently, the origin of “put the wind up” is considered a bit of a mystery. The Oxford English Dictionary is silent on the matter, and most of my reference works don’t even mention the phrase.

In his Dictionary of Slang and Unconventional English, Partridge related (and endorsed) the theory of one of his readers that the phrase comes from a sardonic parody of a standard British Army marching song of the WWI period called “The British Grenadiers.” The “improved” version, popular among enlisted men, contained the lines “Father was a soldier, at the Battle of Waterloo, the wind blew up his trousers, and he didn’t know what to do.” Soldiers sang this song as they marched off to war, and soon, according to this theory, anyone who was flustered or anxious was said to “have the wind up his trousers,” eventually shortened to “have (or get) the wind up.” As Partridge’s correspondent notes, the fact that the song definitely existed, and contained those words, makes this theory highly likely to be true.

That's enough for today.  I don't plan to discuss the other 65 Agatha Christie mysteries; I read them decades ago and had saved just this one for a final reread.