Yes, the avocado plant is toxic to cats. Avocado contains a substance called persin, which is toxic to many animals, including cats. While small amounts of persin are unlikely to cause harm to your cat, if they ingest large amounts of the plant, it could lead to vomiting and diarrhea. Additionally, the pit of the avocado is a choking hazard for cats if they try to play with it or ingest it. It's important to keep avocado plants out of reach of your cat and to avoid feeding them avocado or any other foods that are toxic to cats. If you suspect that your cat has ingested avocado or any other toxic substance, contact your veterinarian immediately.