Default page numbers refer to the UK Doubleday hardback edition, unless stated otherwise.
Note: The 'long dance' of the trolls is likely a reference to the unexpectedly accurate and culturally complex 'long count' of the Mayan calendar.
A curious coincidence is that Tak, the name of the creator in dwarfish mythology, is also the name of an ancient evil spirit featured in two of Stephen King's novels, Desperation and The Regulators (written as Richard Bachman). Like the Summoning Dark, King's Tak comes out of a deep mine and inhabits a human host - in Desperation it is a police officer who becomes a sort of berserker. The similarities go no nearer than that, but it is slightly unsettling.
14 – “Fizz” - the editorial cartoonist in the Times is a reference to Hablot Knight Browne, 19th Century English artist, famous as Phiz, the illustrator of the best-known books by Charles Dickens.
17 – Otto Chriek – “Little, fussy Otto, in his red-lined black opera cloak. . .his carefully cut widow’s peak and, not least, his ridiculous accent. . . .He looked funny, a joke, a music-hall vampire.” - Otto resembles the campy vampire, made famous by Bela Lugosi.
19 – the “Ankh-Morpork Mission of the Uberwald League of Temperance and black ribbons: - A reference to the various temperance organizations in active in the 19th Century in Britain and other countries, such as the Woman's Christian Temperance Movement (which used a white ribbon.) These organizations required members to take a pledge of abstinence from all forms of alcohol. The black ribbons are reminiscent of the scarlet sash worn by members of the Junior Anti-Sex League in George Orwell’s 1984. Similar red ribbons were worn by the Komsomolyet (Коммунисти́ческий сою́з молодёжи) movement - the Soviet Communist Party's youth wing. Nineteenth century slang for someone involved in a temperance movement - or more generally a teetotaler - was a 'Blue Ribboner'.
- Although, naturally, red is the last color a group of reformed B-word addicts would choose for their ribbons!
Sally von Humpeding:- The character's first name is Sally. She is trying to put a suffocating social system that offers little scope for amusement (Vampire society) behind her. She enjoys a drink and a laugh. There is a hint of a cheerful sexual promiscuity, possibly even bisexuality. She is described as boyishly-built with short bobbed black hair.
Is there more than passing reference here to the character and personality of Berlin club singer and performer Sally Bowles, made immortal by Liza Minelli in the film of Christopher Isherwood's Berlin memoir I am a Camera, (filmed as Cabaret)? Taking the thought a stage further, this likens Ankh-Morpork to 1930's Berlin, a city riven at the time by marches and street fighting between the far-right Nazis and the far-left Communists. The Dwarfs are certainly confronted with a populist right-wing politician with a finger firmly pointed at a scapegoat group (Trolls), who advocates their extermination and isn't above murdering fellow Dwarfs to advance his aims...
- [p. 29] "Fred had looked retirement in the face, and didn't want any (as described near the end of Feet of Clay.) Vimes had got around the problem by giving him the post of custody officer, to the amusement of all (As in 'Ol' Fred thought he said custard officer and Volunteered!' Since this is an example of office humour it doesn't have to be funny), and an office in the Watch Training School."
There is a similarity between the above and a scene in the film Aliens, where Hudson comments about Vasquez (one of his fellow Marines): "Yeah, someone said alien, she thought they said illegal alien and signed up". The Vasquez character is supposed to be of Latin American descent, and the Marines are the United States Colonial Marine Corps so Hudson is taking a dig at her origins. I doubt either Colon or Vasquez found the jokes very amusing.
30 – Colon: “Have you heard of Mr Shine?” Vimes: “Do you clean stubborn surfaces with it?” - A reference to Mr. Clean cleanser, a product made by Proctor and Gamble. Or possibly, given that Pterry is British, to Mr Sheen brand of cleaners and polishes made by Reckitt Benckiser.
- [p. 31] "...Koom Valley. Gods damn the wretched place..."
32 – “Koom Valley Day” - Koom Valley Day and the ongoing theme of the dwarves and trolls reliving an ancient battle again and again is reminiscent of the parades held in Northern Ireland by Unionist and Republican groups. The largest of these are usually held by Protestant organizations on the twelfth of July in commemoration of the Battle of the Boyne. The Republican parades celebrating the Easter Rising can be large, but are not nearly so provocative, as they are not deliberately routed through Loyalist areas.
- [p. 34/US p. 25] "That pea-brained idiot at the Post Office has only gone and issued a Koom Valley stamp!"
A slightly obscure cross-book joke: In Going Postal, Moist von Lipwig handed over handling of the issuing of new stamps to Stanley, who is said on (US p. 33) of said book to have been "raised by peas", a "[v]ery unusual case. A good lad [...], but he tends to twist toward the sun, sir, if you get my meaning." Thus, "pea-brained" is here not so much an insult as a descriptor.
- [p. 37] "And just when the day couldn't get any worse, I've got to interview a damned vampire."
So what we have here is an Interview With A Vampire.
42 – Sir Reynold Stitched, curator of the Ankh-Morpork Royal Art Museum, is a reference to 18th century British painter, Sir Joshua Reynolds.
It has also been suggested that there is a strong resemblance, in voice and manner and aesthetic, to Roundworld art critic Brian Sewell (of the London Evening Standard, of the hernia-inducing Sunday heavy papers, and a frequently used pundit on those late night TV arts shows like "Newsnight Review" and "The South Bank Show"). Read his surname as "Sew-Well" in the (non)-seamstress Sandra Battye sense, and it can be seen how he mutates into "Reynold Stitched").
For a sample of the real-life Reynold Stitched in action as art critic, try this:-
42 – The Battle of Koom Valley painting –A cyclorama is a panoramic painting on the inside of a cylindrical platform, designed to provide a viewer standing in the middle of the cylinder with a 360° view of the painting. The intended effect is to make a viewer, surrounded by the panoramic image, feel as if they were standing in the midst of a historic event or famous place. Panoramas were invented by Irishman Robert Barker, who wanted to find a way to capture the panoramic view from Calton Hill in central Edinburgh, Scotland. He subsequently opened his first cyclorama in Edinburgh in 1787. Cycloramas were very popular in the late 19th century. (from Wikipedia)
48 – painting of The Goddess Anoia Arising from the Cutlery - A reference to The Birth of Venus by Sandro Botticelli. Unfortunately for Nobby, it does not have an urn or plinth in it, but there are two cherubs.
- [p. 48/Corgi p. 57] "The title was The Koom Valley Codex."
The whole craze about people buying this book claiming secret messages in a painting is an obvious reference to The DaVinci Code, which claims that there are secrets hidden in the Mona Lisa. The DaVinci Code is a work of fiction, though, whereas The Koom Valley Codex seems to be a nonfiction book. However, the reader's attention is drawn to the Holy Blood and the Holy Grail by Michael Baigent and Richard Leigh, which in the 1980's enjoyed a certain vogue and later on served to inspire The DaVinci Code. (Dan Brown's character Leigh Teabing is a direct homage to HBHG's authors). In these books, the authors link together a set of historical puzzles and anomalies, including the claim that occult secrets are encoded in a series of well-known paintings, to support the hypothesis that Jesus Christ did not actually die on the cross. (In fact, he was resuscitated from near-death, and smuggled to the South of France by Joseph of Arimathea to live out a quiet life in retirement. He married Mary Magdalene, and their bloodline not only became that of the Kings of France, it persists today in exceptionally able or gifted people around the world.) If true, this claim would have the effect of wholly discrediting Christianity, and that the truth has thus been suppressed by generations of Popes. It's worth noting that one of the authors has since acknowledged that the content of the book was a hoax. 
More obscurely, the obsessives who searched Rascal's painting for clues are reminiscent of the real-life searchers (Masqueraders) who'd tromped all over England looking for a jeweled-hare pendant from 1979 to 1982, guided by clues they'd found (or imagined finding) in Kit Williams' picture book "Masquerade". As in Thud!, the hare was initially found by searchers who'd resorted to unscrupulous methods (murder by the deepdowners, milking Williams' ex-girlfriend for hints by the hare's "finders"), but their fraud was exposed and the treasure retrieved/protected from them.
- [p. 57/Corgi p. 68] "War, Nobby. What is it good for?" he said.
"Dunno, sarge. Freeing slaves, maybe?"
"Absol- Well, okay."
A reference to the popular song by Edwin Starr, whose refrain goes, "War: What is it good for? Absolutely nothing". It has been covered by countless bands since then.
Nobby's suggestions that war might be good for freeing slaves or for defending yourself against a totalitarian aggressor appear to refer to the American Civil War and World War II, often considered just or worthwhile wars for those reasons.
Also - to my mind at least - a clear reference to the famous scene in Monty Python's The Life of Brian, when Reg (the leader of one of the innumerable rebellious groups that infest Judea) asks "What have the Romans ever done for us?" and is then more than exasperated when his (equally anti-Roman) collaborators proceed to enumerate about fifteen immensely impressive achievements of the Romans that have made life far better for the peoples they have subjugated.
59 – “Do not . . . what do they call it. . . go spare?” “Spare - adj. British. Out of control, furious. The word usually in the form ‘go spare’ has been in use since before World War II. It derives from the notion of excess.” From “The Dictionary of Contemporary Slang” by Tony Thorne (Pantheon Books, New York, 1990). (from http://www.phrases.org.uk/bulletin_board/9/messages/572.html)
- [p. 62] "I am the Dis-Organiser Mark Five, "The Gooseberry™"..."
The BlackBerry is a wireless handheld device. A "gooseberry" is an unwelcome intruder on a romantic assignation; a fifth wheel.
- [p. 63] "Then would you like to engage the handy-to-use Bluenose™ Integrated Messenger Service?"
Bluetooth is an industrial specification for wireless personal area networks. A "bluenose" is a Whitehousian crusader against pornographic ("blue") material, particularly one that is suspiciously good at locating said material in order to be offended by it. These two jokes are evidently Pterry having a little dig at the irony that "social" media devices are often (mainly?) used for the twin purposes of ruining human interaction and solo sex.
- [p. 63] "How about a game of Splong!™, specially devised for the Mark Five?" pleaded the imp. "I have the bats right here."
Probably a reference to Pong, possibly the very first graphical video game, which was similar to ping-pong/table tennis.
- [p. 63] "My iHUM™ function enables me to remember up to one thousand five hundred of your all time—"
iTunes is a digital media player application developed by Apple Computers, for playing and organizing digital music and video files, and for transferring them to its iPod portable MP3 players. There's also a reference to LucasArt's iMUSE™ technology, which changed the music throughout some of its most popular third-person adventures, like Indiana Jones and the Fate of Atlantis and predated the iPod by a significant amount. Also note that the word itself is "iHUM"; we can assume that the imp simply hums the tune in question rather than replicating it exactly. It also suggests, if one is prepared to mentally squint, the polite euphemism used to describe their trade by Assassins: they inhume rather than murder. Does this suggest that the imp is perfectly capable of murdering a tune, rather like those ever-so-subtly not-quite-right MIDI files which digitize otherwise quite nice tunes and turn them into a sort of lift muzak? (Shades of the robotic Sirius Cybernetics Corporation Company Choir in Douglas Adams' h2g2 singing Share and Enjoy a flattened semi-fifth out of tune).
- [p. 69] "[...] he noticed the symbol chalked on the wall over the door: a circle, with a horizontal line through it."
The "Long Dark" rune, the symbol for a mine, is the same shape as the sign for the London Underground. This may be foreshadowing to the Patricians plans for the Devices, such as mining carts loaded with people (wink wink).
74, 93 – The “Following Dark” symbol which Helmclever makes with his spilled coffee (explained by Carrot later) is a circle with two diagonal lines through it. This is similar to British roadsigns meaning “No Parking.” - [p. 83] "There were twists and turns, in dim tunnels that all seemed alike."
Referring to the text-based computer game Colossal Cave Adventure, which contains the memorable line "You are in a maze of twisty little passages, all alike".
110 – The Breccia - a rock composed of sharp fragments embedded in a fine-grained matrix (as sand or clay) (Merriam –Webster) and also Ankh-Morpork`s version of the Mafia.
112 – Chrysoprase “Kew Eee Dee” - a phonetic version of QED (quod erat demonstrandum) meaning “Thus it is proven.”
114 – Chrysoprase – “And dey cuts Slab wi ‘ bad sulphides an’ cooks it up wi’ ferric chloride and crap like dat. You thought that Slab was bad? You wait till you see Slide.” - This could be a reference to the introduction of crack cocaine. - No wonder ferric chloride has a nasty effect on trolls' silicon brains. It's used to cut circuit boards.
151 – “the clacks company” – Discworld version of a telegraph or fax machine and is based on “A semaphore telegraph, optical telegraph, shutter telegraph chain, Chappe telegraph, or Napoleonic semaphore is a system of conveying information by means of visual signals, using towers with pivoting shutters, also known as blades or paddles. Information is encoded by the position of the mechanical elements; it is read when the shutter is in a fixed position. These systems were popular in the late 18th - early 19th century.”(Wikipedia)
— "That’s a feast for vurms." — A Feast for Wormes was a 1620 book of poems by English poet Francis Quarles. The titular poem related to human mortality, and the title itself has entered the language as a sort of memento mori akin to "ashes to ashes". Quarles' title is most probably a reference itself to Henry IV, Part One where the line started by Hotspur and finished by Hal is -"no, Percy, thou art dust And food for--" "...for worms, brave Percy..."
— “And, incidentally, tomato ketchup is not a vegetable,” Sybil added. — In 1981, the U.S. Food and Drug Administration attempted to reclassify tomato ketchup and pickle relish as vegetables rather than condiments for school lunch programs. The goal was to relax nutritional requirements and cut costs. The measure met with resounding disapproval and was eventually rejected.
Though the book describes Special Constable Hancock's 'new Truncheon' as something very similar to Japanese Nunchukus (usually pronounced "Nunchucks"), the word "numb-nuts" is an insult as well.
169-170 (Harper Torch paperback edition) The footnote describing Empirical Crescent, built by Bloody Stupid Johnson: "On the outside it was a normal terraced crescent of the period, built of honey-colored stone with the occasional pillar or cherub nailed on. Inside, the front door of No. 1 opened into the back bedroom of No. 15, the ground-floor front window of No. 3 showed the view appropriate to the second floor of No. 9, and smoke from the dining-room fireplace of No. 2 cane out of the chimney of No. 19."
Reminiscent of the tesseract house in Robert Heinlein's "And He Built A Crooked House" where the stairs that should lead to the roof deliver you to the ground floor, going out the front door puts you on the second floor and various windows show views of other rooms in the house, a view straight down the side of the Empire State Building (even though the house is in California),an upside down seascape, absolute nothingness and a strange desert landscape.
178 - Sally: “Well here’s another fine mess.”- A variation of the catch phrase from Laurel and Hardy: “Well, here’s another nice mess you’ve gotten me into.”
181 – Nobby: “‘Tawnee’s actually only her pole name,’ Nobby said. ‘She says no one would be interested in an exotic dancer with a name like Betty. She says it sounds like she’d be better with a bowl of cake mixture.’” Possibly a reference to Betty Crocker cake mixes, but also a reference to a famous (at the time) stripper Betty Howard. There is also Forties/Fifties burlesque perfomer Betty Page, a woman still rated as an icon today (her dark beauty inspires Goths) and who has inspired the acts of modern burlesque strippers such as Dita von Teese.
192 - “Brick thought. . . the future was looking so bright that he had to walk along with his eyes almost shut. . .” A reference to the 1986 hit by Timbuk 3 “The Future’s So Bright, I Gotta Wear Shades”.
193 - Pseudopolis Yard – a reference to Scotland Yard, headquarters of the Metropolitan Police Service in London, England.
p199: Vimes is reflecting on the military axiom couldn't tell if it were arseholes or breakfast time. Vimes considers that however confused he got through lack of sleep, he'd still be able to tell the difference, as "only one involves coffee". Vimes has so far not heard of a coffee enema, then. Maybe his ignorance should be cherished.
Gabbro is a kind of igneous rock.
214 – the game Thud - The game was developed by Trevor Truran, Bernard the stout, Cunning Artificer to the Gentry, and Terry Pratchett. The game is based on games of the Tafl family, which are distinguished by the unequal size of the opposing forces. The objective is usually for the force of fewer numbers to take all the members of the larger forces whose aim is generally to stop them doing so. A fragment of a gaming board of 18 x 18 squares, found in Wimose, Fyn, Denmark dated prior to AD400 is the first evidence of a game called Tafl, which also regularly appears in the early Icelandic sagas. (from http://www.tradgames.org.uk/games/Tafl.html)
- [p. 215] "Water dripping on a stone, dissolving and removing. Changing the shape of the world, one drop at a time. Water dripping on a stone, Commander."
This entire exchange with Vimes is a nice bit of foreshadowing.
"Who knows what old evil exists in the deep darkness under the mountains?"
There is a hint of Lord of the Rings here: "There are older and fouler things than Orcs in the deep places of the world." And: "They delved [...] too deep, and disturbed that from which they fled: Durins Bane."
- [p. 238] "'But it's pretty much a 24/8 job for us,' said Angua."
24/7 is the usual phrase (24 hours a day, 7 days a week), but it can be easy to forget that the Discworld week contains 8 days. Worth noting too that many European countries have eight days in a week, the current day and then the next seven to get back to the same day. The Welsh word for week is "wythnos" meaning eight nights.
- [p. 243] In the immediate aftermath of the attempt to kill not just Vimes but also Sybil and Young Sam, a nervous deputation of dwarfish civil dignitaries visits Pseudopolis Yard at least partially to assure Vimes they had no part in it. Vimes, under the influence of the vengeful and vindictive Summoning Dark, is in no mood to be diplomatic and his first instinct is to humiliate these Dwarfs. His inner dialogue at this point is a stream of hateful invective: You scum, you rat-sucking little worm eaters! (etc., for half a page of internalised diatribe)
It is interesting that American TV cop Sledge Hammer not only thinks like this, he speaks and acts like this - all the time. In fact, one of Sledge's favourite pieces of invective to a suspect is a variation on a theme of "scum-sucker".(Or even yoghurt-eater.) Sledge Hammer is a parody on Dirty Harry, with all the knobs turned up to way past eleven... but this cop-with-issues, played for laughs admittedly, must have at some point contracted the Summoning Dark! Now I'm still looking for any instance of Vimes saying Trust me, I know what I'm doing...
Sledge is generally prevented (by restraint or persuasion) from causing extreme mayhem, by his totally-opposite-to-the-point-of-cliché partner. Sergeant Dori Doreau is a thoughtful, gentle, liberally inclined policewoman who acts as the brains of the outfit, while Sledge provides the muscle. Later in the book, Angua and Cheery assume the Doreau role to Vimes' Sledge, and bring him back to rational normality from a beserker-like frenzy.
- [p. 249/US paperback p. 258] "Turd races in the gutter... ...with the name Poosticks".
A reference to the game of Pooh-sticks from the Winnie the Pooh stories, where the characters have races with sticks floating under a bridge. Also mentioned at this point is 'Tiddley-rats', the Ankh-Morpork gutter version of Tiddlywinks.
- [p. 253] "There's throwin' up and yellin' and unladylike behavior and takin' their vests off and I don't know what. 'S called...' he scratched his head '... minge drinking."
Close, Fred. It's Binge Drinking. "Minge" is also (UK?) slang for female pubic hair.
274 – Constable Visit-the-Ungodly-with-Explanatory-Pamphlets with his door-to-door evangelical zeal is a reference to Roundworld Jehovah’s Witnesses, who distribute their religious pamphlets in a similar manner. His god, Om’s, name is a mystical or sacred syllable in the Indian religions, including Hinduism, Sikhism, Jainism, and Buddhism.
290 - Detritus’ crossbow, “The Piecemaker” - A reference to the Convair B-36 (nicknamed Peacemaker), a strategic bomber built by Convair and operated solely by the United States Air Force (USAF). Or maybe to the Colt.45 Single Action Army...
- [p. 290/Corgi p. 352] "Something happens at thirteen miles an hour. I don't know what."
The speed limit and flaming cabbages is probably a nod to the Back To The Future films, where the DeLorean traveled through time when it reached 88 mph, leaving flaming trails behind it.
- [p. 294/UK paperback p. 356] "He pulled out a battered volume entitled Walking in the Koom Valley, by Eric Wheelbrace..."
Punning on the walker, author, and illustrator Alfred Wainwright.
- [p. 298] "The roads up there are pretty bad, you know,' said Vimes.
'So I believe, sir. However, that will not, in fact, matter."
Another possible reference to Back To The Future, in particular Doc Brown's line: "Roads? Where we're going, we don't need roads".
- [Audible part2, 2:55:18] "... Brick, who had not picked a good day to go cold turkey, it was turning out to be frozen Roc."
Aside from the rock (stone) / roc (giant mythical bird) pun in the punchline, the setup is also funny as a reference to the "Looks like I picked the wrong week to quit smoking/drinking/amphetamines/sniffing glue!" running gag by the air-traffic control tower supervisor from Airplane! (the 1980 movie). This may not have been intended, but the scene does involve a rough landing of a flying vehicle (into cabbages).
301 - Sybil’s friends from the Quirm College for Young Ladies “all seemed to have names like Bunny or Bubbles” – a reference to stereotypical British public-school girls' nicknames.
- [p. 305/Corgi p. 368] "The other thing he noticed was that the landscape ahead was strangely bluish, while behind them it had a relatively red tint."
This is a reference to the blue- and redshift, a physical phenomenon caused by the Doppler effect. When you move towards an object, the observed wave propagation speed of the light emitted by that object is reduced by your own velocity. A lower propagation speed, while retaining the frequency, results in a smaller wavelength. Therefore, given the right speed, something green in front of you is observed as blue (-> blueshift). The speed of approximately one hundred miles per hour, at which the coach drives, is far too low for the effect to be observed, but the allusion is a clear one. This may also be justified by the fact (mentioned in several earlier books) that Discworld light travels a lot slower than Roundworld light.
328 – “Quis custodiet ipsos custodes” - a Latin phrase from the Roman poet Juvenal, which literally translates to “Who will guard the guards themselves?”, and is variously translated in colloquial English as “Who watches the watchmen?”, “Who watches the watchers?”, “Who will guard the guards?”, “Who shall watch the watchers?”, “Who polices the police?” or other similar translations. Made famous in the Graphic novel the Watchmen by Alan Moore. The slogan is seen and heard throughout the novel, on the basis that the Watchmen are vigilantes that operate outside of the law where protective checks and balances exist, so there is no oversight to what they might do. For example Rorschach kills most of the bad guys he comes across, as did the Comedian. Sent to prison, and recognised by criminals he allowed to live so as to do time, Rorschach neatly turns the tables on their revenge attack on him, and slaughters the lot in a manner most courts would consider crosses the border from legitimate self-defence into cold calculated murder. (One attacker, a criminal of dwarf stature, is used to block a toilet - head-first - so as to flood a cell wing. Rorschach then uses the combination of ankle-deep water and lots of bare metal fittings to electrocute a dozen more.) (Wikipedia)
344 - '"This is just the story of the Things Tak Wrote", Cheery whispered to Vimes'
This must have been a loud whisper, as a couple of pages previously, Vimes had sent Cheery back to the town.
- [p. 348] "Bashfullsson rose, looking shocked and massaging his hand. 'It is like using an axe,' he said, to no one in particular, 'but without the axe...'"
Right at the end of the book, Colon and Nobbs are on guard duty in the Cave of the Kings. After discussing the state of play between Nobby and his pole-dancer girlfriend Tawneee, Colon, perhaps by association of ideas, reins in an over-enthusiastic Dwarf with the rebuke "No touching, sir, or I'm afraid I shall have to cut your fingers orf". Almost as if he were acting as bouncer in a pole-dancing club, where there is usually a strict rule about touching...