Poison: every materiel which has a potential to affect physiological activity of an organ of a pet’s body can be a poison.
Poisonous materials can be absorbed via digestion: chocklate , inhalation :carbon monoxide, skin : arsenic, injection: overdose medications.This brief article is about indigestion of a poison.
Generally people assume chemical materials as toxic substance however this is a mistake and every materials such as medications and even  food materials can be toxic. For example humans can use chocolate or grape without any problem but for in dogs they cause poisoning.
If a pet eats unusual material which can affects it’s health, it is better to refer it to a veterinary hospital to induce emesis-vomiting- as soon as possible. In general it takes about two hours for a toxic material to pass stomach and enters the small intestine. In small intestine materials are absorbed. When a poison is in the stomach emesis is useful.
The speed of exit from stomach for liquids is more than solid materials. Therefor liquid poisons need immediate attention.
It is necessary to say that emesis is not a general rule for every eaten poison.For some poisons emesis not only useful but also is harmful like bleach.
Generally a dog or a cat has less than two hours to get rid of a toxic substance by emesis. After that because of poisoning your vet should use protocol of fighting with clinical signs of this problem and in this situation the chance of treatment depends on the toxic substances.