Things that are dangerous to dogs

Apple Cores
As the seeds contain Cyanogenic Glycosides which can result in cyanide poisoning pear seeds are the same
Apricot stones contain CG as well so do Cherry stones Plum stones and Peaches

Anti Freeze
This is not only found in cars it is used in garden water features ti keep the water de iced
Instant Baby
Foods Before feeding any baby food to your dog check the ingredients to see if it contains onion powder, which can be toxic to dogs. Feeding baby food in large amounts may result in nutritional deficiencies.

Cooked Bones
Can be very hazardous for your dog. Bones become brittle when cooked which causes them to splinter when broken. The splinters have sharp edges that have been known to become stuck in the teeth, caused choking when caught in the throat or caused a rupture or puncture of the stomach lining or intestinal tract. Especially bad bones are turkey and chicken legs, ham, pork chop and veal.
Raw bones (uncooked in any way) are great and a good sorce of calcium and help keep your dog's teeth healthy by removing plaque. A caution - bones have a high calcium content and too many can cause severe constipation so feed with oil unless your Bevs sister
Bread Dough
When bread dough is ingested your dog's body heat causes the dough to rise in the stomach. During the rising process alcohol is produced as the dough expands. Dogs who have eaten bread dough may experience abdominal pain, bloat, vomiting, disorientation and depression. A pet needs to eat only a small amount to cause a problem, because bread dough can rise to many times its size.
Caffeine
Beverages with caffeine (like tea, coffee) acts as a stimulant and can accelerate your dogs heartbeat to a dangerous level. Dogs drinking caffeine have been known to have seizures, some fatal.
Sugarless Sweets and gum
Sugarless sweets and gum containing xylitol has been recognized to be a risk to dogs This compound can cause liver damage and death in some dogs. This information is recent and some vets may not be familiar with xylitol poisoning.

Cat Food
Cat food is not formulated for canine consumption. It is generally too high in protein and fats and is not a balanced diet for a dog

Chocolate
Chocolate contains theobromine, a compound that is a cardiac stimulant and a diuretic. When affected by an overdose of chocolate, a dog can become excited and hyperactive. Due to the diuretic effect, it may pass large volumes of urine and it will be unusually thirsty. Vomiting and diarrhea are also common. The effect of theobromine on the heart is the most dangerous effect. Theobromine will either increase the dog’s heart rate or may cause the heart to beat irregularly. Death is quite possible, especially with exercise. Symptoms of chocolate poisoning include: vomiting, diarrhea, tremors, hyperactivity, irregular heartbeat and seizures.
Larger quantities of chocolate can poison or even kill a medium or large dog. An ounce or two of chocolate may not seem like much but it can be lethal to a small dog that weighs 10 lbs. or less. After their dog has eaten a large quantity of chocolate, many pet owners assume their pet is unaffected. However, the signs of sickness may not be seen for several hours, with death following within twenty-four hours.
Cocoa powder and cooking chocolate are the most toxic forms. These forms of chocolate contain ten times more theobromine than milk chocolate. Even licking a substantial part of the chocolate icing from a cake can make a dog sick. The next most dangerous forms are semi-sweet chocolate and dark chocolate, with milk chocolate being the least dangerous. A dog needs to eat more than a 250gm block of milk chocolate, however the high amount of fat found in milk chocolate can lead to an attack of pancreatitis.

Corn Cobs
Many dogs have suffered and, in some cases, died after eating corn-on-the-cob, because the corn cob caused a partial or complete intestinal obstruction. Never allow your dog access to corn cobs.

Dairy Products
Most dairy products are digested poorly by dogs who have little or none of the enzyme required to digest the lactose in milk. Just like lactose-intolerant people, lactose-intolerant dogs can develop excessive intestinal flatulence and may have foul-smelling diarrhea. It is best to avoid most dairy products altogether, although small amounts of cheese or plain natural yogurt are tolerated by most dogs, since these products have less lactose than most.

Grapes and Raisins

Although the minimum lethal dosage is not known, grapes and raisins can be very toxic to dogs when eaten. The symptoms are gastrointestinal signs including vomiting and diarrhea, and then signs of kidney failure with an onset of severe kidney collape I personally have not known a dog recover they usually die from kidney failure

Liver
Many dog treats and prepared foods contain liver so it may surprise you to find liver on the bad foods list. In small amounts liver is good for your dog, but if the liver intake is too high it can cause nutritional problems because liver has a high content of vitamin A. Consumption of this vitamin in large amounts can lead to vitamin A toxicity, or hypervitaminosis A. If your dog eats raw liver or consumes three servings of cooked liver a week it could lead to bone problems. Feeding liver to a dog taking Vitimin A supplements can lead to an overdose of Vitamin A.
Symptoms of hypervitaminosis A are deformed bones, excessive bone growth on the elbows and spine, weight loss and anorexia. If left unchecked, hypervitaminosis A has in some cases caused death.
Onions
Onions cause hemolytic anemia, which means that the red blood cells break down leaving the dog short of oxygen. Onion poisoning can occur with a single ingestion of large quantities or with repeated meals containing small amounts of onion. The condition generally improves once the dog is prevented from eating any further onion. The poisoning may occur a few days after the dog has eaten the onion. At first dogs affected by onion poisoning show gastroenteritis with vomiting and diarrhea, weakness and show little or no interest in food. The red pigment from the burst blood cells appears in an affected dog's urine making it dark colored. The dog will experience shortness of breath because the red blood cells that carry oxygen through the body are reduced in number. Other symptoms are elevated body temperature, confusion, and increased heart rate
The quantity of onions, raw or cooked, required is high enough that dogs can generally tolerate small doses of onions without any problem and moderate amounts of onion without apparent signs of onion poisoning. All forms of onion can be a problem including dehydrated onions, raw onions, cooked onions and table scraps containing cooked onions . Left over pizza, Chinese dishes and commercial baby food containing onion,
While garlic also contains the toxic ingredient thiosulphate, it seems that garlic is less toxic and large amounts would need to be eaten to cause illness.
Salt
Iodized salt and salty food can cause stomach problems and pancreatitis Some dogs especially large breeds have been known to drink too much water after eating salty food and have developed a life threatening condition called bloat.

Water
Bet you are surprised to see this listed but there are dangers in stagnant water in ponds bogs lakes and some canals

If I have missed anything feel free to add
Val