Gnolls are small, gangly, vaguely dog-like creatures. They like garbage, a lot. They give meaning to the word Garbologist. They eat it, live in it, and collect it. And they are very territorial about their garbage. They make great go-fers, run-arounds, and garbage men, but are generally not cut out for the business world. Most people don't like their lawyer or doctor to smell like streets of Ankh-Morpork. They can't smell like the sewers, the Morpork side at least doesn't have any.