Observe Your Dog's Behavior
If you think your dog has eaten something poisonous, but his behavior is normal and he isn't showing any symptoms, stay calm. Call your vet, and give him any information you can about the substance your dog has ingested.
Remember that while some foods, like chocolate and onions, can be toxic to dogs, they may not necessarily be harmful if ingested in very small quantities.
Danger Signs
If your dog is having seizures, is losing or has lost consciousness, or is having difficulty breathing, don't bother with poison control. Rush him to an emergency veterinary clinic.
When Poison Control Can Help
If your dog has just ingested a poisonous substance, and is beginning to show symptoms, call poison control for advice. They can help you administer emergency first aid, but are no substitute for treatment by a qualified veterinarian.