Pets sneak under the dining table, begging for treats, and they're hard to resist. But many of our favorite foods are poisonous to pets, and sharing can make them sick and even kill them.

"Many people don't understand how dangerous human foods can be to their pets," says Tom Ricks, DVM and a member of the American Veterinary Medical Association. "But common foods can make them sick, or even kill them, and it often doesn't take much," he told Newsmax Health.

1. Alcohol. Yes, the commercial where the dog brings its master a can of beer is cute, but alcohol — beer, wine, or liquor — can damage a pet's brain and liver just like it can damage yours. And since dogs and cats are so much smaller than we are, a little can make them sick — only a tablespoon can cause major problems in cats. In addition to avoiding giving them a sip on purpose, clean up any spilled drinks quickly.

2. Chocolate. Although it's tempting to give your pet a bite of your chocolate, even small amounts can make them sick. Chocolate contains theobromine, an alkaloid, and dark chocolate, since it contains higher amounts of theobromine, is more dangerous for your pet in smaller amounts. In dogs, chocolate can cause vomiting, seizures, rapid or irregular heartbeat, diarrhea, and muscle tremors. In cats, chocolate can cause heart problems, muscle tremors, or seizures. Only a couple of M&M's can be deadly for a bird. Chocolate can kill within 24 hours.

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3. Nuts. Although pets may beg for nuts, some are particularly poisonous to dogs, including macadamia nuts and walnuts. Symptoms include vomiting, weakness, hyperthermia (elevated body temperature), and pale gums that occur within 24 hours. Nuts covered with chocolate are especially toxic and can lead to kidney failure and death.

4. Apple seeds and cherry pits. Dogs crunching on an apple don't leave the core with its seeds on the floor — they gulp down the entire apple. And those seeds contain cynanide, which is also found in peach, plum, apricot, and cherry pits.

5. Onions. Onions contain a chemical called thiosulphate that is very toxic to dogs. The chemical can build up in the dog's body, destroying red blood cells and causing anemia. Cats are also susceptible to the effects of onions, and small amounts can cause digestive problems. "Even one small green onion can make a cat very sick," Ricks said. Garlic is also toxic to both cats and dogs. Symptoms of poisoning include diarrhea and difficulty breathing.

6. Grapes and raisins. Grapes and raisins can cause sudden kidney failure in both cats and dogs. Symptoms, which occur within 24 hours, include diarrhea, vomiting, decreased urination, and lethargy. Since raisins are more concentrated, it takes fewer to cause harm — about half an ounce can be toxic for a cat or small dog. The effects are cumulative, so eating a few grapes or raisins over a period of time can be fatal.

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7. Candy or gum containing Xylitol. The common artificial sweetener Xylitol, found in diet candy and gum, stimulates the pancreas to produce more insulin, which causes blood sugar to drop to dangerously low levels in dogs and cause liver damage that can be fatal. Symptoms can become obvious within 30 minutes, and the dog may become uncoordinated and vomit.

If you believe your pet has ingested a poisonous food, contact your veterinarian immediately.