1. The stimulants contained in chocolate and caffeine can cause vomiting and diarrhea, says Rebecca Remillard, DVM, Ph.D, a board-certified veterinary nutritionist at Angell Animal Medical Center.
2. Human-grade canned tuna is high in fat and magnesium and, if eaten in excess, can cause yellow fat disease. A lack of antioxidants causes this fatal disease, which breaks down body fat, says Daniel Carey, DVM, of IAMS Co., Dayton, Ohio.
3. Chopped liver contains large amounts of vitamins A and D, which in excess can result in painfully malformed bones. "But cats would have to eat it almost exclusively for weeks," Dr. Remillard says.
4. Some houseplants - such as poinsettias dieffenbachia, azaleas, Christmas cherry and ivy - may be harmful to cats if ingested in large quantities, says Rolan Tripp, DVM, an affiliate professor of applied animal behavior at Colorado State University Veterinary School, Ft. Collins, Colo. "It is a dose per pound of cat issue." A small kitten playing with and consuming many leaves is a problem. A good-sized cat merely nibbling any of these is not cause for panic."