Here's an analogy I thought up to help other people think about Transubstantiation. Suppose you invent a machine that converts margarine molecule-by-molecule to butter. The margarine looks, tastes, smells, feels and acts like butter. But it's not butter, since butter and margarine have different natures. Anytime someone or something loses any essential property, the loser becomes something of another kind. A wood chipper changes a tree limb into wood chips, death turns a body into a corpse, a fire reduces a log to ashes.