Quote from : Men at Arms Book

Vimes stared. It was true about the dogs. There didn't seem to be quite so many mooching around these days, and that was a fact. But he'd visited a few dwarf bars with Carrot, and knew that dwarfs would indeed eat dog, but only of they couldn't get rat. And ten thousand dwarfs eating continuously with knife, fork, and shovel wouldn't make a dent in Ankh-Morpork's rat population. It was a major feature in dwarvish letters back home: come on, everyone, and bring the ketchup.