In the end few pages of Thud, Rhys, King of the Dwarves is speaking to the Grag and says...
"One does not make demands of Kings..."
He's referring to Sam Vimes, who's asked Rhys for something in return for stopping a war in Koom Valley. Rhys is wondering why Sam isn't asking for gold or silver and the Grag is saying that Sam is insistent and the city dwarves will be right behind him.
What is this 'thing' that Sam is asking for? I can't find it!! It's driving me nuts!