Dogs can be poisoned by medicines, foods, chemicals, plants and many other substances. Different poisons affect the body in completely different ways. Some cause vomiting or neurological symptoms quickly, while others can damage the liver or kidneys before the dog looks obviously ill.
Remove whatever is left and try to identify the product. Keep the packaging, the list of ingredients or a photo of the plant if relevant. Estimate how much your dog may have taken in and when. This information helps the vet decide whether decontamination, tests, an antidote or monitoring is needed.
Contact a vet right away if you suspect poisoning, even if your dog still seems normal. Do not make your dog vomit and do not give salt, milk, oil, charcoal or other home treatments without explicit instructions, as the wrong measure can make the situation worse.