Cats should not eat grapes. Although the specific toxic substance in grapes is unknown, ingestion can lead to symptoms like vomiting, diarrhea, lethargy, and in severe cases, kidney failure. The toxicity of grapes in cats is less common and less well-documented than in dogs, but the risk is still present, so it is safest to avoid feeding grapes or raisins to cats altogether. Cats do not need grapes in their diet, and since they are obligate carnivores, grapes have no nutritional benefit for them. Additionally, grapes can also pose a choking hazard to cats. In summary, grapes are potentially harmful to cats and should be kept away from them to avoid health risks. If a cat ingests grapes, monitoring for illness and consulting a veterinarian promptly is advised.