The basic texture of meat, dense and firm, comes from the mass of muscle fibers, which cooking makes denser, dryer, and tougher. And their elongated arrangement accounts for the “grain” of meat. Cut parallel to the bundles and you see them from the side, lined up like the logs of a cabin wall; cut across the bundles and you see just their ends. It’s easier to push fiber bundles apart from each other than to break the bundles themselves, so it’s easier to chew along the direction of the fibers than across them. We usually carve meat across the grain, so that we can chew with the grain.