now that's odd...

Okay, I picked up the new Discworld book, "Thud", and quite enjoyed it. I plan on re-reading it today. However, I was thinking about various Discworld characters and plot threads that have been introduced in various books and then used in other books (there are a few in "Thud"), and the following passage popped into my head. (Note: I do not think this is in any Discworld book. I think part of my brain made this up and told the rest of my brain so it could gauge a reaction.)

Mr. Rope turned and looked at the thief. "And if I don't pay your fee to roam the streets safely?"
"Ah, well, it would be incumbent upon me to point out that the streets aren't exactly safe, now are they?"
Mr. Rope flexed his hands. They were quite large hands, and when he flexed them there was a sound not unlike walnuts being cracked open. There were, in fact, no walnuts present, but the thief, in a horrible burst of imagination, could, in fact, see the walnuts that were not there.
"Or, perhaps, we could both find different alleys to be in?" the thief brought up.
"I like this alley."
"Ah."