"Aagrahgaah," said Detritus mournfully.
"Don't mind me, just don't spit it on my boot," said Vimes.
"It mean-" Detritus waved a huge hand, "like... dem things, what only come in..." he paused looked at his fingers, while his lips moved "...fours. Aagrahgaah. It mean lit'rally der time when you see dem little pebbles and you jus' know dere's gonna be a great big landslide on toppa you and it already too late to run. Dat moment, dat's aagragaah."
Vimes's own lips moved. "Forebodings?"
"Dat's der bunny."
"Where does the word come from?"
Detritus shrugged. "Maybe it named after der soun' you make just as a t'ousand ton of rock hit you."
- Jingo, by Terry Pratchett, page 13 (from the top, after Leshp has reappeared, and they're watching the people in Sator Square harangue and such. I'm telling you, RTWT)