" We —I mean to say we mammals — who in general do not have problems about obtaining water, have learned to wedge it into the urea molecule, which is soluble in water, and as urea we free ourselves of it; other animals, for whom water is precious (or it was for their distant progenitors), have made the ingenious invention of packaging their nitrogen in the form of uric acid, which is insoluble in water, and of eliminating it as a solid, with no necessity of having recourse to water as a vehicle. In an analogous fashion one thinks today of eliminating urban garbage by pressing it into blocks, which can be carried to the dumps or buried inexpensively. "

― Primo Levi , The Periodic Table