Cats can safely eat small amounts of apple flesh as an occasional treat, but the core, seeds, stem, and leaves of apples contain cyanide and can be toxic to cats. It is important to remove these parts and wash or peel the apple to avoid pesticide exposure. Apples are not a necessary part of a cat's diet since cats are obligate carnivores and get their nutrients from meat-based foods. Overfeeding apples or giving processed apple products (like applesauce with sugar or dried apples) is not recommended due to potential digestive upset and the risk of obesity or diabetes. Overall, small, plain pieces of apple flesh are generally safe in moderation, but always avoid the toxic parts and consult a vet if unsure.