I was just browsing through some articles on dog food ingredients when I stumbled across a page on what foods are toxic to dogs.
I delved in a little deeper and found out these amazing facts:

Chocolate especially cocoa powder and cooking chocolate has theobromine in it which increases activity of the heart in dogs and elevates the rate of urination.
If a dog is affected by this it could become very hyperactive, vomit, have diarrhoea, need to urinate alot and will probably be very thirsty.
The most dangerous symptom is the increase in the dogs heart rate which can be fatal.
Sometimes you may not see any change in the dog until a few hours later and by then it could be too late.

Onions can also be fatal to a dog because they have thiosulphate in them.
If eaten your dog may vomit, have diarrhoea, lose their appetite, be breathless, have blood in urnine and act very weak and lethargic.
Garlic also has thiosulphate in it but it is less toxic than onions
Any amount of onion whether cooked or raw is not good for your dog, having small amounts often is just as bad as having a large amount once or twice.

Macadamia nuts are another human food that is bad for dogs.
Macadamias can cause paralysis of the hind legs, swollen limbs and give the dog pain when the legs are touched

If your dog does eat any of these things I suggest you see or at least call your vet right away.

I knew that chocolate is deadly to dogs but I was really surprised to read about the onion, garlic and macadamias.
In the past I have given both of my dogs our dinner scraps but since reading about that I have stopped.
I would rather have them give me those desperate puppy dog eyes for my scraps and say no than not have them in my life!

For more information check out my article on dog food ingredients.