The stems, leaves, seeds, and peels of citrus fruits can be dangerous to cats, as they contain varying levels of citric acid and essential oils that can be irritating to a cat's nervous system. These parts of the citrus fruit can also contain other compounds that may be toxic to cats. For example, citrus leaves and stems contain a chemical compound called psoralen, which can cause photosensitivity and skin irritation in cats. Additionally, citrus seeds contain small amounts of a toxic compound called amygdalin, which can cause gastrointestinal upset and even cyanide poisoning in cats if ingested in large amounts.