I found a chewed-open packet and my pet seems totally fine — do I wait for symptoms?

Call your vet or your nearest emergency clinic now and go in. Do not wait for symptoms.

With most poisons there is a silent window in which the animal looks completely normal while the damage is quietly being done, and treatment given inside that window is dramatically more effective, and far cheaper, than treatment given once a dog or cat is visibly ill.

Do not try to make your pet sick yourself. Home methods are unreliable, several are dangerous in their own right, and with some substances — anything caustic, anything petroleum-based — bringing it back up causes a second, worse injury on the way out. Making an animal vomit is a decision, taken with proper drugs, by a vet who knows what was swallowed and when.

Take with you the actual packet, plant or pill bottle, even chewed and torn. Add roughly how much was in it, roughly how much is left, the time it happened, and your pet's weight. That exact set of facts is what your vet's toxicology reference needs in order to tell you whether this is nothing or everything.

Things that are far more dangerous than people expect: chocolate, grapes and raisins, sugar-free gum and sweets sweetened with birch sugar, human painkillers of every kind, antifreeze, rodent bait, onions and garlic, and, for cats, lilies, where even licking pollen off the fur can destroy the kidneys.

Products and their formulations differ between countries, so your vet or emergency clinic can look up your exact one, and in many regions they can also consult a dedicated animal poison service. Bring the label; it does half the work.