VCA Animal Hospitals. According to their website, one or two dark chocolate or baking squares is enough to be fatal for an adult cat who ingests it, and as little as one ounce of milk chocolate can kill a kitten if ingested.
Symptoms of chocolate poisoning in cats include vomiting, hyperexcitability, nervousness, and diarrhea. In severe cases, the only sign may be sudden death. It's very important that you call your veterinarian, a local emergency veterinary hospital, or the ASPCA Animal Poison Control hotline for advice if you think your cat has ingested chocolate.
Onions and Garlic: Onions and garlic are not good for cats as they can cause gastrointestinal upset and red blood cell damage, according to the ASPCA.
Xylitol: Xylitol is a sweetener used in many products, such as baked goods and candy. Xylitol can lead to the release of insulin in cats, which leads to hypoglycemia (low blood sugar), and can potentially lead to liver failure. Initial signs of xylitol poisoning include vomiting, loss of coordination, and lethargy. Seizures and recumbancy may also occur. Elevated liver enzymes and liver failure may occur within a few days of ingestion.
Grapes and Raisins: According to the ASPCA, grapes and raisins can cause kidney failure in pets who have ingested them.
Amaryllis: Amaryllis is also known as St. Joseph lily, Belladonna lily, Naked Lady, and Cape Belladonna. When eaten, Amaryllis may cause hypersalivation, depression, abdominal pain, vomiting, diarrhea, lack of appetite, and tremors.
Mistletoe: Mistletoe or American Mistletoe is also toxic to cats. When ingested, mistletoe can cause gastrointestinal distress, breathing difficulties, low heart rate (bradycardia), erratic behavior, vomiting, diarrhea, and cardiovascular collapse. Low blood pressure can also occur when cats eat this plant, but it is rarely seen.
Poinsettia: Poinsettia may cause mouth and stomach irritation as well as vomiting for cats who ingest it.
Please note that this list of food and plants is not all-inclusive. There are many other human foods and plants kitties should not eat.
If you know that your cat has ingested any of these foods or plants, please contact your veterinarian, local emergency veterinary clinic, or the ASPCA Animal Poison Control hotline for advice on how to handle the situation. There is a $65 consultation fee the ASPCA Poison Control Center hotline. Their number is 888-426-4435.