What you need to know:
Recently, I had a 95 lb. Great Pyrenees present after ingesting a whole box of chocolates. The owner had called ahead and I was prepared to induce vomiting, start on IV fluids if necessary and provide supportive care. When he arrived, the dog had a normal physical exam - normal temperature, attitude, heart rate, etc. Luckily, the owner brought the box that had contained the chocolates.
What I like to do with any potential toxicity is have the owner call one of the animal Poison Control Centers before or upon arriving at our hospital. He called ASPCA Poison Control Center and gave them the information they needed e.g. the dog's age, weight, breed, etc., time of ingestion and the ingredients on the label of the box.
I then got on the phone and talked with a veterinarian at the Center describing my findings on the physical exam. I was surprised to learn that the dog had not ingested a toxic dose despite ingesting the whole box - mainly because he was a large dog. She said that we might notice some gastrointestinal signs such as vomiting or diarrhea, but shouldn't notice any of the more severe signs of toxicity - increased thirst/urination, restlessness, increased heart and respiratory rates, increased temperature, muscle tremors, seizures, coma and even death with a severe toxicity.
We kept the dog for observation the rest of the day with no treatment and he did fine.
Veterinarians commonly get calls from pet owners about possible toxin exposure. We are somewhat familiar with the more common exposures, but we aren't aware of everything that might be toxic to pets or whether the amount ingested is likely to be a problem. The same amount of chocolate ingested by a 10 lb. dog might have caused a serious toxicity. These poison control centers have a large data base as well as technicians and veterinarians available who deal with toxicities everyday.
What You Need To Do:
You should visit one or both of the following Poison Control Centers to familiarize yourself with them before you need them, but also to peruse the wealth of information about things that can be toxic to your pets:
Pet Poison Helpline (855-764-7661)
ASPCA Poison Control (888-426-4435)
If your pet is not showing any symptoms or ill effects after a possible exposure to something and you're unsure if it's harmful or not, you can call one of the Poison Control Centers and/or your vet. Who knows, the substance might not even be toxic to pets or the amount ingested may not be enough to pose a serious threat. The staff at the Poison Control Center can usually advise you whether to take your pet to your veterinarian for treatment or not.
If your pet is showing signs of illness and you find evidence of an exposure to a harmful substance (e.g. an empty, obviously chewed upon box of chocolates), be sure to take the evidence with you to the vet, so that an accurate diagnosis/prognosis can be determined and proper treatment prescribed.
There is a charge (see amount on their website) when you call one of these Poison Control Centers. But, in my opinion, it is well worth it because it could save you an unnecessary trip to the vet. If your pet needs treatment for the exposure, their staff can give your veterinarian guidance on the treatment needed to have the best possible outcome for your pet. There is usually no charge for followup calls if your veterinarian needs further assistance during treatment.
On a related topic, I found this article about common reasons for pet insurance claims during the Christmas season.