14 Surprising Pet Poisoning Dangers

While the health perks of garlic are well known for humans, all veggies in the Allium family can cause serious damage to your dog or cat's red blood cells, causing them to burst. Other consequences include anemia and kidney damage. Weakness and an upset stomach are signs your pet may have ingested garlic, onions, shallots, or leeks. Raw is more dangerous because the active ingredient is more concentrated, but cooked is also harmful. (Don't worry if you see onion or garlic powder listed in your pet's food—they're harmless in powder form.)

Though dogs love this sweet treat, it can be deadly. "The important thing to know is that milk chocolate is much, much less toxic," says Steven Hansen, president and CEO of the Arizona Humane Society and board certified veterinary toxicologist. "The most toxic is baking chocolate, then high-quality dark chocolate." The cocoa beans in chocolate contain theobromine, a chemical that's toxic in small animals. It can cause an increased respiratory rate, central nervous system disorders, vomiting, diarrhea, seizures, cardiac failure and even death. A potentially lethal dose for a 16-pound animal is two ounces of baking chocolate or 16 ounces of milk chocolate. One sweet treat you don't have to worry about: white chocolate. That's because white chocolate doesn't contain cocoa solids, and therefore only trace amounts of theobromine.

Though it isn't understood why, raisins and grapes can cause life-threating kidney failure in dogs. (Cats don't typically eat raisins and grapes—they tend to steer clear of sweeter foods.) Vomiting and diarrhea can start as early as four to six hours after eating them, and typically begin within 24 hours.

As few as five or six of these nuts can a kill dog, thanks to an unknown toxin. They can cause seizures, depression, vomiting, and trouble walking—their rear legs can appear to be paralyzed. "It's very dramatic and quite scary, but if they are treated right away the outcome is they recover within 48 to 72 hours," says Hansen. Typically, the vet will pump the dog's stomach and induce vomiting to clear out the macadamia nuts. Dogs may also be put on IV fluids in the hospital.

Dogs and cats can't process xylitol, an artificial sweetener commonly found in sugarless gum, the same way humans can. It affects their glucose levels and causes their blood sugar to drop so quickly that they can die from it. It can also lead to seizures and liver damage at fatal levels. Plus, if dogs sniff out gum, "sometimes they will eat the whole packaging and can get an obstruction from the material," cautions Halligan.

The pits in plums, peaches, and cherries, as well as apple seeds, aren't just a choking hazard or an object that could get stuck in your pet's intestines. The pits also contain cyanogenic glycosides, which are cyanide-like compounds that can lead to difficulty breathing, excess salivation, shock, seizures, and coma in both dogs and cats.

"If your dog gets into the garbage can and eats some moldy cheese, it can lead to neurological problems, like trembling," says Hansen. It also puts your furry friend at risk for toxicity, thanks to the tremorgenic mycotoxins found in moldy bread, pasta, cheese, nuts, and other foods. Watch out for vomiting, agitation, stumbling, tremors, and seizures.

"Caffeine is the toxic ingredient here, so decaf would probably just cause diarrhea," says Halligan. Caffeine contains methylated xanthines, which stimulate the central nervous system, meaning the heart can be overstimulated and lead to death. Ingesting caffeine can also cause vomiting.

Related: 12 Surprising Sources of Caffeine

Avocados are high in heart-healthy monounsaturated fat—but those fats are only healthy for humans. For your pets, the high fat content is bad news since it can cause an upset stomach, vomiting, and eventually pancreatitis (inflammation of the pancreas). And if your dog or cat eats the pit, it can get lodged in their intestines and cause a blockage.

"Every day in this country, some unsuspecting pet owner gives his pet a pill in the hope of making his dog or cat feel better, often with disastrous results," says Halligan. "Prescription and over-the-counter medications can be lethal to pets; they don't process drugs the same way humans do." Acetaminophen can be fatal to dogs and cats because they lack the necessary enzymes to detoxify and break it down, leading to blood cell and tissue damage. Symptoms develop quickly and include weakness, salivation, vomiting, difficulty breathing, dark-colored urine or gums, and abdominal pain.

Two regular aspirin can kill a cat or a small dog. "Although it can be used safely as an anti-inflammatory in cats and dogs in appropriate dosages, it has the potential for serious side effects," says Halligan. Cats are at a greater risk than dogs because they are deficient in the enzymes needed to metabolize this drug. Outward signs of aspirin toxicosis in cats include incoordination, depression, lack of interest in food, vomiting, loss of balance, bloody diarrhea, and panting. Cats may also develop severe anemia, bleeding disorders, and kidney failure. The signs for dogs are gastrointestinal problems, respiratory difficulties, neurological problems, bleeding disorders, and kidney failure.

Vets prescribe anti-inflammatories to relieve muscle and joint pain, but the doses for pets are much smaller than for humans, says Halligan. That means you don't want your pets getting their paws on your bottle. "Cats are extremely sensitive to the toxic effects of NSAIDs due to their higher gastrointestinal absorption rates and decreased ability to metabolize these drugs," Halligan says. They can cause life-threatening ulcers and bleeding disorders, and also reduce blood flow to kidneys and other organs, causing significant damage and bone marrow suppression. NSAIDS include ibuprofen (Advil, Motrin) and naproxen (Aleve).

Houseplants can help you breathe easier by giving off oxygen and removing chemicals like formaldehyde from the air, but if your curious cat or dog takes a nibble, it could prove deadly. Eating a small amount of a mildly toxic plant isn't always fatal, but large or repeated doses can be extremely dangerous, especially for cats. "Given the huge number of plants in existence, it's impossible to know every single plant that may be toxic to your pet," says Halligan. "As a general rule, plants that are listed as toxic to humans should also be considered toxic to animals." The five most dangerous plants are lilies, azaleas, oleander, sago palm, and castor bean. Hansen also cautions that pets may want to play with—and chew on—bouquets, so keep an eye on those too. Signs of ingesting plants include vomiting, diarrhea, frequent urination, and drinking lots of water.

Dogs will eat just about anything you leave on the counter, including marijuana, says Hansen. Though it won't kill your dog, you should take Fido to the vet right away if he's eaten your pot. "They will recover with treatment but it can last several days," Hansen says. Look for incontinence, weakness, lethargy, stumbling, low heart rate, dilated pupils, and sometimes vomiting.