Lilies are toxic to cats because they contain a yet unidentified toxin that specifically causes severe kidney damage in cats. All parts of true lilies (Lilium species) and daylilies (Hemerocallis species) are poisonous, including the petals, leaves, pollen, stems, and even the water in a vase with cut lilies. Ingesting even small amounts of any part of these lilies can lead to acute kidney failure, which can be fatal if not treated promptly. Cats can be poisoned by chewing on the plant, ingesting pollen from licking their fur after brushing against the plant, or drinking lily-contaminated water. This toxin affects cats uniquely and does not cause the same kidney failure in other pets like dogs. The exact chemical responsible for the toxicity remains unknown, but the result is rapid and often irreversible kidney injury in cats after ingestion.