Many common human foods are toxic to dogs and can lead to severe health issues or even be fatal. Here are some of the most hazardous foods:

1. Chocolate: Chocolate contains caffeine and theobromine, which can affect the central nervous system and heart of dogs. Dark and baker’s chocolate have the highest levels of these compounds and are particularly dangerous. 

   Symptoms of chocolate poisoning can include vomiting, diarrhoea, seizures, and in severe cases, heart failure and death​​.

2. Grapes and Raisins: The specific toxin in grapes and raisins is unknown, but ingestion can lead to kidney failure in dogs. 

   Symptoms include vomiting, diarrhoea, lethargy, and decreased urine production​​.

3. Xylitol: This sugar substitute, found in sugar-free gum, candies, and baked goods, causes a rapid release of insulin in dogs, leading to hypoglycemia (low blood sugar). 

   Symptoms can appear within 30 minutes and include vomiting, weakness, seizures, and liver failure​​.

4. Onions and Garlic: These contain compounds that can damage dogs' red blood cells, leading to anaemia. Consumption in any form (raw, cooked, or powdered) can be harmful. 

   Symptoms include weakness, vomiting, and breathlessness​.

5. Macadamia Nuts: Like grapes and raisins the specific toxin in macadamia nuts is unknown however Ingestion can cause the following:

   Symptoms: weakness, depression, vomiting, tremors, and hyperthermia, these symptoms usually appear within 12 hours and can last up to 48 hours​.

6. Avocado: Contains persin, which can cause vomiting and diarrhoea in dogs. 

   All parts of the avocado plant (fruit, seed, bark, and leaves) contain persin and should be avoided​.

7. Alcohol and Yeast Dough: Alcohol can cause serious health issues in dogs, including vomiting, diarrhoea, decreased coordination, and central nervous system depression. Yeast dough can expand in the stomach, causing bloating and potentially life-threatening torsion.​ 

    

8. Milk and Dairy Products: Many dogs are lactose intolerant, if they consume milk or dairy products Gastric upset can occur.

   Symptoms: digestive upset, including diarrhoea and vomiting

9. Fatty Foods and Bones: High-fat foods can cause pancreatitis in dogs, and bones can splinter, causing choking or internal injuries.

    

10. Citrus Fruits: Contain citric acid, which in large amounts can cause central nervous system depression. Small amounts might only cause an upset stomach​.

To keep your dog safe, it's essential to keep these foods out of reach and be cautious about feeding them any human food without consulting a veterinarian. If you suspect your dog has ingested any toxic substances, contact a veterinarian or a pet poison control centre immediately.