I think “an entire large onion” or “one chocolate bar” are surprisingly large amounts, because my default assumption when something is called poisonous is that any amount is dangerous.
An onion or a chocolate bar is not that much, unless your dog is tiny. And no, the dose makes the poison, that’s the basic principle of toxicology. Anything can kill you, you can die from even drinking too much water too quickly.
My point is that if you give your dog some of your human food and there turns out to be a little bit of garlic in it, your dog is in no danger. Many people don’t know that. I’m not challenging basic principles of toxicology or claiming that a dog can’t possibly eat enough of these foods to be poisoned. If your small dog eats a chocolate bar or a whole bag of onion rings, you should probably do something about that.
Also, the following isn’t a reply to what you said but I just remembered it and I thought it might be useful information for some dog owners. Swallowing even a little bit of dilute hydrogen peroxide from the pharmacy will quickly make a dog vomit. It took less than a teaspoon for my 30-pound dog. I would start with a teaspoon and then he spilled a lot while I was trying to make him swallow it. I had to resort to this several times when he ate something dangerous.
IMO this is generally safe (but do your own reading and take your own dog’s specific issues into account) and even if it’s not ideal, it’s something useful for those dog owners who would have difficulty spending hundreds of dollars on surprise vet bills. Some vets will tell you not to do it, but in my experience, many vets will recommend way too much medical treatment for dogs, often to the point that it is a waste of money and sometimes even to the point that it harms the dog.
