Fish (fresh and canned)
If you feed fish to your cat that is intended for human consumption, it can cause malnutrition as it lacks proper feline nutrients. It can also cause a thiamine deficiency, not to mention the danger of bones which can cause an obstruction.
Caffeine (from chocolate, coffee, or tea)
Caffeine can affect the heart and nervous system and can be toxic.
Chocolate
In addition to caffeine, chocolate contains theobromine, a compound that is toxic to cats.
Fat and bones
Both fat and bones may be dangerous for cats. Fat, both cooked and uncooked, can cause intestinal upset, with vomiting and diarrhoea. And a cat can choke on a bone. Bones can also splinter and cause an obstruction or cut the inside of your cat's digestive system.
Grapes and raisins
Just as small amount can make a cat ill as they contain an unknown toxin which damages the kidneys.
Macadamia nuts
Also contain an unknown toxin which can affect the digestive and nervous systems.
Too much milk and other dairy products
Just like humans, some cats cannot break down the lactose in milk. This can result in gastrointestinal upset.
Mushrooms
Some contain toxins that affect multiple systems in the body, cause shock, and result in death. So, avoid them all!
Onions and garlic (in all forms)
These contain sulfoxides and disulphides, which can damage red blood cells and cause anaemia.
Potato, rhubarb and tomato leaves and stems, green tomatoes, and potatoes
These foods are members of the nightshade family, and contain the poisonous alkaloid glycoalkaloid solanine, which can cause violent lower gastrointestinal problems. So, it’s important to keep them away from veggie gardens when they are outdoors.
Sugar-free lollies and gum
These can contain the sugar substitute xylitol, which is toxic to cats.
If you suspect your cat has eaten something it shouldn’t, always contact your vet immediately.
Source: rspca.org.au