Avocados are dangerous, partly due to a fungicidal toxin called persin. Only high doses are lethal, but mild symptoms like vomiting and diarrhea can occur from consuming smaller portions.
Apples
The flesh of apples is not toxic, but the seeds can be poisonous due to a compound called amygdalin. However, they have to be consumed in large quantities and chewed to be toxic.
Garlic
Garlic can be fatal to dogs due to a compound called thiosulfate that damages red blood cells. It takes a lot of garlic to cause toxicity, but some breeds are particularly sensitive
Milk and other dairy
Even though milk and dairy products have calcium-boosting properties, they can be bad for dogs and contribute to levels of lactose intolerance. This can cause a lot of discomfort
Macadamia nuts
In general, nuts are not good for dogs, especially macadamia nuts. These are ranked as the most toxic, which can lead to vomiting, weakness, hyperthermia, and loss of bodily functions.
Mustard
Mustard won't be lethal to dogs in small doses, however, it can be toxic in higher amounts. In fact, due to mustard’s mild toxicity, it's often something that’s suggested by vets
Artificial sweetener
Xylitol is a sugar alternative found in human foods such as candy and many baked sweets. It’s extremely toxic to dogs, causing rapid insulin release within 15 to 20 minutes
Chocolate
Chocolate contains a stimulant called theobromine, which is poisonous to dogs. The amount of theobromine depends on the type of chocolate. It mainly affects the gut, heart, nervous system
Onions
Onions can be poisonous to dogs due to the thiosulfate they contain. Certain dog breeds are more vulnerable, and their size makes a huge difference.
Cooked bones
Giving your dog a raw, uncooked bone to chew on is great, but avoid cooked bones. These can easily splinter and in large quantities cause constipation or perforation, which can be fatal.
Grapes and raisins
Grapes and raisins rank among the most serious food threats for dogs. Small amounts can even cause sudden kidney failure, and commonly cause vomiting and diarrhea.
Caffeine
A small amount of caffeine won't do any harm, but if your dog swallows a handful of coffee beans or tea bags then it can pose serious danger.