The scene that proved that despite having plenty of raw power, it's her grasp of headology that makes Granny Weatherwax really dangerous:
Granny Weatherwax: Are you watching, Mrs Gogol? Are you watching real close?
In short: Gogol threatens Granny with a Voodoo Doll of her, and Granny responds by shoving her arm in a brazier, causing the doll to burst into flames, while she's unhurt.
Granny: That's headology. It's the only thing that matters. Everything else is just messin' about.
Granny and Lilith are imprisoned in Lilith's mirrors. Lilith faces exactly the same choice as Granny does below. "She ran on through the endless reflections." But Granny has a better grip on her identity:
Granny Weatherwax: Where am I? Death:Inside the mirror... Granny Weatherwax: When can I get out? Death:When you find the one that's real. Granny Weatherwax: Is this a trick question? Death:No. Granny Weatherwax: This one. Points to herself
Vampires have risen from the dead, the grave and the crypt, but have never managed it from the cat.
Also, Greebo scaring the living crap out of the "mousie" and the transformed horses.
"And the trouble with small furry animals in a corner is that, just occasionally, one of them's a mongoose."