You may share your backyard and even your bed, but it’s probably best to avoid sharing a meal with dogs, or any other pet for that matter.

Listed here, from most (1) to least (4) dangerous, are common foods and drinks that make pets sick. If you think your dog, cat, or bird has consumed one of these items and you are concerned, contact your veterinarian.

1. Chocolate
Why: Stimulates the nervous system and the heart. Poisonous to: All species, but dogs are most likely to eat dangerous quantities. Possible effects of poisoning: Vomiting, increased thirst, restlessness, agitation, increased or irregular heartbeat, increased body temperature, tremors, seizures.

2. Grapes, Raisins
Why: Damage the kidneys. Poisonous to: Dogs, cats. Possible effects of poisoning: Increased thirst, increased urination, lethargy, vomiting.

3. Garlic, Onions
Why: Damage red blood cells, causing anemia. Poisonous to: Cats, dogs. Possible effects of poisoning: Vomiting, red-colored urine, weakness, anemia.

4. Xylitol (Found in sugarless gum.)
Why: Causes increased insulin secretion, resulting in lower blood sugar levels. Poisonous to: Dogs. Possible effects of poisoning: Vomiting, lethargy, lack of coordination, seizures, jaundice, diarrhea.

5. Alcoholic Drinks

Why: Depress the nervous system. Poisonous to: All species. Possible effects of poisoning: Vomiting, disorientation, diarrhea, lethargy, lack of coordination, difficulty breathing, tremors, coma, seizures.

6. Raw Yeast, Bread Dough

Why: Forms gas in the digestive track; fermentation of yeast causes alcohol poisoning.
Poisonous to: All species, but only dogs typically ingest it. Possible effects of poisoning: Distention of abdomen, vomiting, disorientation, diarrhea, lethargy, lack of coordination, difficulty breathing, tremors, coma, seizures.

7. Macadamia Nuts

Why: Cause muscle and nervous-system problems. Poisonous to: Dogs.
Possible effects of poisoning: Vomiting, lethargy, weakness, increased body temperature, tremors.

8. Avocados

Why: Contain persin, which damages the heart muscle. Poisonous to: Most species―birds are especially sensitive.
Possible effects of poisoning: Vomiting, diarrhea (in dogs), lethargy, difficulty breathing (in birds and rodents).

The pet-food ingredient labels are usually incomprehensible.

There is little research on important questions such as these. For instance, there is hardly any research on the question of longevity of pets based on their diets, whether they were fed raw, vegetarian, premium or complete and balanced pet-food products. The pet-food companies don’t conduct this type of research!

Mainstream pet-food products often get a bad rap.

If you feed your pet a complete and balanced product, it will meet your pet’s nutritional needs.

These products are all the same, from a nutritional standpoint. And if you’re doing that, your pets do fine. That’s the great contribution of the pet-food industry — they’ve given consumers a cheap, convenient product that keeps their pets alive. We found no evidence that complete and balanced pet food is harmful to pets, except where mistakes have been made in the course of production.

What do terms like natural, human-grade and premium mean when describing pet food?

Here you run into exactly the same problems you have with human food, where there’s no official regulatory definition for terms like natural and premium.

In pet food, human-grade means all the ingredients meet the standards you set for human-food production. We visited a facility which was used to manufacture human food on some days and pet food on others. Very few pet foods are allowed to use this term.

What’s the most important thing to look for on a label?
Ingredients. If you’re dealing with a complete and balanced pet food, the nutrients in it will be adequate, because they meet a standard. So the only difference among these products is what the ingredients are. In the book we recommend that pet-food labels be changed to resemble human-food labels so that they’re easier to understand.

Why does some pet food contain ash?
It’s not like the stuff you take out of fireplaces! The ash in pet food refers to minerals.

What ingredients, besides chocolate, should pets not eat?
Onions, garlic and macadamia nuts are the main ones, but little bits are unlikely to be harmful.

Is there concern that BPA and other chemicals used in sealing canned foods are harmful to pets’ health? There’s certainly a great deal of concern, but there’s no research on it whatsoever.

Can cats be vegetarian?
Cats are carnivorous, but there’s plenty of research that shows they’re perfectly capable of digesting grains, as long as they also get the amino acids, vitamins and minerals they need. Dogs are fine with grains too. In fact, most complete and balanced pet-food products contain grains.

Should you let your cat drink out of the toilet bowl?
It is not advisable it for cats or dogs. Toilet water is likely to be contaminated. Even though dogs and cats don’t get sick from salmonella the same way humans do, you still don’t want to expose your pets to unnecessary germs.

Feed Your Pet Right: The Authoritative Guide to Feeding Your Dog and Cat (Free Press, 2010), written with Malden C. Nesheim, professor emeritus of nutritional sciences at Cornell University.