" Waste not, want not’ is the Engineers’ motto, Miss. Properly processed human ordure makes very useful fuel for our city’s engines. And we are experimenting with ways of turning it into a tasty and nutritious snack. We feed our prisoners on nothing else. Unfortunately they keep dying. But that is just a temporary setback, I’m sure. "

― Philip Reeve , Mortal Engines (Mortal Engines, #1)