Chocolate contains Theobromine, which is toxic to cats, even in small amounts, as well as caffeine, another no-no.
Onions contain N-propyl disulphide which causes anemia and, thereby, jaundice (yellow discoloration in lips and eyelids, as well as skin in light-skinned cats). A toxic dose for the average cat would be a couple slices, so watch those onions!
3. Uncooked potatoes & tomatoes
Both these plants come from the deadly nightshade family. Eaten raw, they are likely to cause cats gastrointestinal distress. Cooked tomatoes and potatoes, however, have no toxic effects. (Eating green potatoes, cooked or not, can cause cardiac issues, hallucinations and paralysis, but as they are bitter this is not likely to be an issue.)
4. Milk & milk products
As kittens, cats can drink cow’s milk, but as they grow up cats become intolerant to lactose, a sugar found in cow’s milk, and can no longer digest dairy products. Even a few laps of milk or a tidbit of cheese can cause gastrointestinal pain and diarrhea in adult cats. Lactose-free milk or live culture yogurt, however, can be given at any age.
5. Yeast dough
The ingestion of yeast dough can cause severe abdominal pain, intestinal rupture, and even alcohol poisoning as the dough rises and expands and the yeast ferments.
6. Grapes & raisins
Grapes and raisins may cause kidney failure, vomiting, and diarrhea in cats.
7. Caffeine & alcohol
This one may seem obvious, and chances are these beverages would never end up in a cat dish, but if a curious cat were to lap the dregs out of a coffee cup or get into an open saucepan of penne vodka sauce, the consequences would likely be fatal as there is no cure for caffeine or alcohol poisoning in cats. Three tablespoons of 40 percent liquor is enough to prove deadly.
8. Garlic & chives
Like onions, garlic and chives can also cause anemia and gastrointestinal problems in cats. In small amounts, chives are sometimes included in commercial cat food. While this may not be enough to cause problems, don’t let your cat mistake your window box of chives for a planter of cat grass.
Xylitol is an artificial sweetener found in candy, gum, and even some toothpastes. Xylitol will produce seizures in cats soon after ingestion and liver failure a day or so after, so keep your gum out of kitty’s grasp.
– See more at: http://moderncat.com/articles/9-foods-never-give-your-cat/65600?utm_source=Modern+Cat+Enewsletter&utm_campaign=b63dc8e073-MC_Mewsbite_08_21-14_internetcats&utm_medium=email&utm_term=0_1380895f1f-b63dc8e073-64162005#sthash.GBaeKQaA.dpuf