If you're feeling curious, let's get a little technical for a second. From a botanical standpoint, hay is typically made from the stalks and leaves of plants, while grains are the seeds or fruits of those same plants. It's a subtle difference, but an important one when it comes to understanding the nuances of agriculture.
Think of it like the difference between apples and apple seeds. Both come from the same plant, but they're used in different ways and have different properties. Similarly, hay and grains come from the same plant world, but they're used for different purposes and have different characteristics.