Maybe due to the milk in chocolate. They are lactose intolerant.

Also grapes, oranges and sour apple.

Not really. My dog loves apple. My neighbour's dog loves oranges.

Read somewhere that too much raisins/grapes will cause kidney failure or something like that. There are too many cases where dogs died caused by this toxic.

Anyone free enough to Google?

Raisins/Grapes = Toxic

Now, there you go...

Grape and Raisin Toxicity in Dogs

Others i know of :

Chocolate = Heart Attack
Onion/Garlic = Red blood cells burst
Macademia nuts = Muscle weakness

Pls note, eating a piece or 2 does not cause the above effects.
Only in large quantities. (Experts test with a cup)
Also, smaller the dog, less the amount needed to kill.

I used to do alot of research on dog health as I took a course.
Someone will need to Google to get some proof.

No, I realised its not the milk in choc. Its the cocoa in chocolate.

I used to have a dog who likes cakes but will throw up if he ate any cream on the cakes...