It's not recommended to feed blueberry muffins or any baked goods to cats, including the muffins that are specifically made for cats. Most baked goods, including blueberry muffins, contain high levels of sugar, salt, and other ingredients that are not suitable for a cat's digestive system. Consumption of baked goods can cause gastrointestinal upset, such as vomiting and diarrhea, in cats. Additionally, blueberries themselves are not toxic to cats, but they do not provide any significant nutritional benefits for cats either. Therefore, it's best to avoid feeding blueberry muffins or any other baked goods to cats and instead stick to a nutritionally complete cat food recommended by a veterinarian to ensure that your cat's dietary needs are being met.