Thud!/Fridge

Fridge Brilliance

 * Angua points out to Carrot, after returning from her trek through the mud, that the when she and Vimes went down into the Long Dark mine with Ardent. Vimes gashed his hand on a nail/rivet on one of the water-tight doors while he was down there. Ardent caught up with him about that moment, quite flustered by Vimes' going down a tunnel without him. Ardent explained it as "this is a mine, there are dangers!" Once you consider the fact that , it adds a little more color to Ardent's sudden concern.
 * 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.
 * Also arguably.
 * 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 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.
 * 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

Fridge Horror

 * At some point, the reader realizes that the graphic featured on the title page and that separates blocks of text throughout the book is the Summoning Dark rune.
 * ...and the second you're TOLD it's a Fridge Horror, it becomes Paranoia Fuel. Thanks much.
 * When reading the Discworld novel , one eventually realizes that the graphic featured on the title page and used to separate blocks of text throughout the book is the Summoning Dark rune,
 * And what happens when you shut the book?
 * Well, as noted above, the Summoning Dark
 * Thank you so very much. Excuse me whilst I go set my copy of Thud! on fire.
 * NO! Don't! Remember the Summoning Dark that Angua painted on the drinks menu? Remember why Vimes can't just burn it? Because that sets the Summoning Dark free and releases it into the world