When cats eat grass, it generally reflects instinctual behavior with several possible reasons behind it. Cats may eat grass to aid their digestion, help expel indigestible materials like hairballs, feathers, or bones they swallow while grooming or hunting, and sometimes to induce vomiting to relieve an upset stomach. Grass can also serve as a natural laxative to help cats pass stool, especially if they are constipated. Another reason is that grass might provide certain nutrients such as folic acid that cats need, or simply because some cats enjoy the taste or texture of grass. Evolutionarily, this behavior may have helped wild cats expel intestinal parasites, although domesticated cats likely no longer need this protection. Eating grass is usually safe, but care should be taken to ensure the grass is free from pesticides or toxic plants. In summary, cats eating grass is a natural behavior with benefits related to digestion, nutrition, and instinctual parasite control.