The dog will not be poisoned soon after eating a small piece of onion. The owner can induce vomiting after the dog has just eaten it. If the dog cannot vomit it out, let the dog drink more water and exercise to increase the body's metabolism and help the onion to metabolize quickly. Excrete it from the body, and then closely observe the dog's physical condition. If symptoms of poor energy and reluctance to move occur, the dog should be sent to a nearby pet hospital for treatment in a timely manner.