Feegles on a broomstick. "And all at once, there was a sound vaguely like AAAAAAAAAAAAAAAAAAAAAAAAAAAARGH!"
At one point, Daft Wullie feels hurt because Rob Anybody said he didn't have the brains of a beetle. Rob cheers him up by apologizing and saying: "Daft Wullie, ye do hae the brains o' a beetle, an' I'll fight any scunner who says different!" Which, one chapter later, leads to this exchange between Granny Weatherwax and Daft Wullie:
Granny Weatherwax: Daft William, there's room in my well for one more frog, except that you don't have the brains of one! Daft Wullie: Ahahaha, that's wholly correct, mistress! I fooled you there! I ha' the brains o' a beetle!
This is made even funnier by the fact that Granny, usually never one to let anyone have the last word in any conversation, does not reply but just glares at him and then changes the subject. That's right — Daft Wullie just managed the impossible feat of saying something so stupid that even Granny Weatherwax couldn't think of a biting reply.