Yes they can eat grapes, and in fact enjoy it. Do not offer asparagus, eggplant or cabbage, raw potato or rhubarb, though as those are damaging.
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ingested by an organism and assimilated by the organism's cells in an effort to produce energy, maintain life, or stimulate growth.
Historically, people secured food through two methods: hunting and gathering, and agriculture. Today, most of the food energy consumed by the world population is supplied by the food industry. Agriculture
Medicinal plants have been identified and used throughout human history. Toxic plants even have use in pharmaceutical development. Angiosperms (flowering plants) were the original source of most plant medicines. Some herbs and spices come from flowering plants.
Topics concerning medicinal plants include: Polygonaceae