Grass cell walls are hard for animals to digest because of lignin, a tough material that holds the walls together. Lignin is controlled in different ways in grasses, and it can vary in how it's connected within the walls. Changing the amount and type of lignin can make grass cell walls easier to break down. Scientists have found that genetic changes can help improve how well animals can digest grass, but the success of these changes depends on the plant's genes and the methods used to study the cell walls.