Grass is a producer, or the very first level of the web. It's role is to provide food for primary consumers, and since it's a producer it also has the role of producing oxygen/ consuming carbon dioxide through photosynthesis. The snake is a secondary consumer, so it would not eat grass but would eat the animals that do. Those might include mice or other small rodents. The roles are similar because they both are crucial parts of the food web, without them the whole thing has the possibility to fall apart. The roles are different however, because grass does not consume other organisms however it makes or produces its own food through photosynthesis.