I'll even add it here just to make it really clear. The exact mass of a random animal or a random object in our universe, it can take on any of a whole set of values. I mean who knows exactly the exact number of electrons that are a part of that object right at that moment. Who knows the neutrons, the protons, the exact number of molecules in that object or part of that animal exactly that moment. So that mass, for example at the zoo, it might take on a value anywhere between, well maybe close to zero. Close to zero. There's no animal that has zero mass.