Foods that are harmful or toxic to cats:
1. Onions and garlic. Onions, garlic, shallots, and scallions can damage a cat's red blood cells, causing anemia. Cats will definitely be poisoned if they eat large amounts of these foods, but they will also be poisoned if they eat onion soup or garlic powder, which are made from concentrated onions or garlic.
2. Raw eggs, raw meat, and bones. Just like humans, cats can become infected with Salmonella or E. coli if they eat raw eggs or raw meat. Symptoms vary and may include vomiting, diarrhea, and lethargy.
3. Chocolate. Chocolate is toxic to cats. It contains a substance called methylxanthine, which can cause symptoms in cats such as vomiting and diarrhea, fever, muscle tremors, abnormal heart rhythm, abdominal discomfort, excessive thirst, and seizures. 
4. Alcohol. Alcoholic beverages and foods are toxic to cats. Ingesting these foods can cause symptoms such as vomiting, diarrhea, disorientation, difficulty breathing, coma, and even death.
5. Milk. Cats cannot digest the lactose in milk, so it may upset their stomachs or cause diarrhea. Except for kittens' mother's milk, it is not recommended to give cats milk.
6. Grapes and raisins. Even small amounts of grapes and raisins can make your cat sick and may even cause acute kidney failure. Vomiting may occur within 12 hours of ingestion. Other symptoms may appear within 24 hours, including lethargy, diarrhea, loss of appetite, abdominal pain, and decreased urination.
