A delicious snack for humans but a not-so-healthy snack for our feline friends. Eating this kind of food can result in kidney failure, especially for those with underlying kidney disease. It's best not to take any risks with renal failure so keep these out of reach of your cat.
Cooked or uncooked, keep these not-so-fun-guys (geddit?) away from your cat. While store-bought mushrooms are likely to cause less damage than wild mushrooms (often toxic and possibly fatal to cats), it's probably best to ban them altogether. Just to make things more difficult - apparently, cats crave mushrooms, despite not being able to eat them at all. Talk about curiosity killing the cat...
Any cat owner knows that cats love this stuff. While a little bit won't be harmful, feeding tinned tuna to your cat on a regular basis can lead to an increased risk of mercury poisoning. It is also high in unsaturated fats (too much can be bad for cats), and can cause Vitamin E deficiency and an inflammation of fatty tissue - a condition known as steatitis.
If you have cats and dogs in the house, don't be tempted to double-up when it comes to dinner time. While the occasional nibble probably won't hurt, make sure your cat doesn't eat dog food on a regular basis as they have different nutritional needs from dogs and can't survive on a doggy diet. The best way to avoid any unwanted mix-ups is to monitor your dog's meal times and make sure the cat doesn't muscle its way in.
Milk and other dairy products
This one's contentious, as it doesn't apply to all cats, but many become increasingly intolerant of lactose as they get older. If milk is given to a cat who has trouble digesting it, it can lead to bloating, abdominal pain and diarrhoea. If you think your cat is one of the few who can still drink milk at an older age, there's a chance you're right - always check with your vet.