- "She prided herself on her unrivaled knowledge of the properties of Ramtops herbage - none knew better than she the many uses of earwort, Maiden's Wish and Love-Lies-Oozing" - Granny is much more of a herbalist here than in Witches Abroad, where Magrat claims that Granny just gives people colored water to make them feel better (Granny makes this claim herself in this book, but Magrat implies that Granny does this because Granny doesn't know more about herbs). Possibly she learned herbalism before she'd figured out Headology, or she uses them to cure animals and/or fellow witches, saving the colored water for those who'll believe in its power.
- "...smelling of anti-moth herbs" - a silly reference to mothballs?
- Granny Borrows bee minds in this book. In Lords and Ladies she specifically says this is very difficult, but manages to do it for the "first time" there. Could be another of those mistakes in time referenced in Thief of Time, or perhaps she could only observe bees' minds at this point, and learned to direct a whole swarm via Borrowing later.
- "You know that. Esk didn't." - Pterry seems to address the reader quite a bit in the book. J.R.R. Tolkien used the same literary device in The Hobbit.
- "All wizards knew ... the important thing about moving something from A to Z, according to basic physics, was that at some point it should pass through the rest of the alphabet." - Ponder Stibbons finally manages to overcome this rule when he teleports Rincewind in Interesting Times
- "...wizard of the third rank or above" - Is 'rank' another word for 'level' here? (Presumably so, given that they're synonymous with each other.)
- "His Adam's apple..." - I wonder how this Discworld phrase originated? Or is it Translation Convention at work? Perhaps, since the gods probably argue about who created the first humans, Discworlders just decided to choose a random male name.
- "According to the standard poetic instructions one should move through a fair like the white swan at evening moves o'er the bay" - a reference to the Irish folk song She Moved Through the Fair, which has slightly different lyrics.
- "The lodgings were on the top floor next to the well-guarded premises of a respectable dealer in stolen property because, as Granny had heard, good fences make good neighbors." - reference to the Robert Frost poem Mending Wall
- "There are two ways of getting into Unseen University [...] The first is to achieve some great work of magic, such as the recovery of an ancient and powerful relic or the invention of a totally new spell" - this line shows that Ridcully didn't just make up this possibility when he presented it to Rincewind in Interesting Times
- Granny makes references to several witches, but doesn't mention Nanny Ogg, even though we later discovery that Nanny and Granny are lifelong friends. (Perhaps she felt that Esk was far too young to be subjected to "The Hedgehog Song"?) Nanny won't make her first appearance until Wyrd Sisters.
- Even though some of the action takes place in the Unseen University Library and the Librarian is present, then-assistant librarian Rincewind is conspicously absent. But given his unwilling tendency towards adventuring, it could be he's off somewhere interesting, moving at high speed.
- "Fiftysevenfiftysevenfiftysevenwell?" - one of the frequent 57 references in TP's work
- And of course the open and veiled references to the old English folk song The Two Magicians, which, as Granny Weatherwax would darkly mutter, refers to goings-on (as most folk songs eventually do). In the song, a wizard pursues a witch, with carryings-on in mind, but she eludes and fights him by continual transformations of herself, to which he responds by continual transformations of himself...
"She became a trout, a trout all in the brook;
But he became a feathered fly, and catched her with his hook!"
Possibly the best version was done by electric folkies Steeleye Span on the LP Now We Are Six.
Three variants of the lyrics and a discussion of the themes (male magic versus female) can be found here:- 
And a brilliantly good animated performance of the song may be seen here. Watch. Appreciate! This is good.
Direct references to Roundworld: