As a Fridge subpage, all spoilers are unmarked as per policy. You Have Been Warned.
Fridge Brilliance
- Angua points out to Carrot, after returning from her trek through the mud, that the dwarf who painted the Summoning Dark rune on the door in his own blood was probably still alive when she and Vimes went down into the Long Dark mine with Ardent. Vimes gashes his hand on a nail/rivet on one of the water-tight doors while he is down there. Ardent catches up with him about that moment, quite flustered by Vimes' going down a tunnel without him. Ardent explains it as "this is a mine, there are dangers!" Once you consider the fact that somewhere down there, one of the miners is slowly dying in the dark because of Ardent and the grags, it adds a little more color to Ardent's sudden concern for Vimes looking around.
- Angua also mentions at the time that there wouldn't be a nail in a metal door, and leaving a rivet/weld sharp enough to cut yourself on is exceptionally poor engineering practice and totally uncharacteristic of dwarfs... and that's in a normal mine, never mind one that is housing grags. The cut isn't from anything physical - it is Vimes being "infected" by the Summoning Dark, in much the same way that it leaves a scar after it retreated from his soul.
- What's the one recognizable feature the Summoning Dark's mental presence and symbol exhibits? A barbed tail. On whatever psychic/mystic/spiritual level it resides, it stung Vimes.
- Arguably, the hypocrisy inherent in the fundamentalist dwarves' attempts to prevent knowledge of the Low and Diamond Kings' message from spreading, when one realizes they were erasing recorded words. Words spoken by the most revered dwarf of all time, B'hrian Bloodaxe, no less.
- One for longtime readers of the series: in the famous "THAT! IS!! NOT!!! MY!!!! COW!!!!!" line... well, look at it. One more exclamation point for each word. Remember how both Reaper Man and Maskerade discussed how adding more exclamation points shows you're getting crazier, and having five exclamation marks is a sure sign of madness? Well, it's a much less comedic use here since it's in the middle of Vimes' climactic struggle with the Summoning Dark, but still...
- It's mentioned in the scene where Carrot, Angua, and Sally are investigating the crime scene that every deep dwarf has a draht, a unique identifier tattooed on their right wrist. The Summoning Dark leaves an "exit wound" scar on Vimes' right wrist - so from now on, any dwarf automatically/reflexively looking for a draht would see the Summoning Dark staring back.
- After Vimes 'cuts' his hand on the 'rivet' in the door (see above), Igor goes on about 'tiny invisible biting creatures' (lisp omitted). Now, imagine that in the form of the Summoning Dark. A tiny invisible biting creature, eating its way into his mind...
- There's a subtle moment during Vimes' talk with Mr. A. E. Pessimal: Vimes explains why he wants to take on the auditor Pessimal as an officer, summing up with 'I want someone who can hold a pencil without breaking it'. This may sound like a frustrated/affectionate jibe at the expense of Vimes' men, who are generally not at home to Mr. Paperwork. But when you notice that just a page previous to the exchange Vimes himself has literally broken his pencil by pressing too hard with it, you realise that it is also self-deprecation.
- When Grag Bashfullsson starts wondering if the Summoning Dark is following the other grags. Later on, we realize that it is. Right inside Samuel Vimes, who is following them.
- When Vimes and co. are bowling along to Koom Valley in the magic coaches, the narrative notes that the landscape ahead looks bluish, while the landscape behind has a "relatively red tint". They're slicing time.
- They were most likely just moving at relativistic speed and are therefore experiencing blueshift and redshift, which also occur when slicing time sufficiently thin. See, the speed of light in a heavily magical environment (such as, for instance, the entire Disc) is quite low. Pratchett even uses "relatively" to describe the redness behind them.
- Notably, light can be Doppler-shifted even without relativity, for the same reason sound can. There's a relativistic Doppler shift effect, yes, but there's a separate effect that takes place even if relativity isn't affecting you. If we wanted to get technical, relativity shouldn't matter as you approach the (comparatively slow) speed of light on the Disc, because relativity only cares how fast you're going compared to the speed of light in a vacuum. You shouldn't actually experience purely relativistic effects like time dilation and length contraction when moving at the speed of light on the Disc, which is implied to be something like a few hundred miles per hour.
- Had Rascal lived anywhere other than Empirical Crescent, the grags' search for the Cube would have been a whole lot easier, as they could have simply dug out the nearest well to the man's residence and found it directly. But thanks to Bloody Stupid Johnson's reality-warping geometric incompetence, an object dropped into a well in that neighborhood might wind up anywhere.
- Except that's not what happened. The Cube is resting at the bottom of the well at Empirical Crescent with no spatial anomalies being present, indicating that B.S. Johnson's "unique" approach to engineering didn't affect the well. The reason the Grags have to dig out half the city's underground to find the Cube is that Rascal didn't just live at Empirical Crescent. His acute paranoia meant that he was constantly changing residence and never wrote down where he was staying or when a given note was written. Vimes maps out the various places Rascal stayed, and they're spread across a sizable chunk of the city. The Grags had no way of knowing where he was when he wrote the note about "throwing it in the well", so they decided to just dig everywhere, using the well in any given area as the place to dig towards.
Fridge Horror
- The graphic featured on the title page and used to separate blocks of text throughout the book is the Summoning Dark rune, representing an unbelievably ancient, quasidemonic entity of pure revenge, summoned with a dying dwarf's last breath in his own blood, that in order to have an effect in the world must choose a champion to possess and inspire killing rampages. What happens when you shut the book? You leave that rune in the dark... Of course, it is in there with the Guarding Dark.
- The Dwarfs fanatically respect the written word and their lore. Yet, at some point since Koom Valley, their priest class has systematically defaced written versions of their origin myth so that the part about Trolls is/was completely reversed in their culture's collective memory. That is/was the depth of their unthinking hatred: to defile everything they claimed to hold sacred in order to retroactively justify that hate. They probably thought they were heroes for doing it, too.
