 Food poisoning usually hits hard with nausea, diarrhea, vomiting, and fever, and it can start within hours of eating. If you decide that leftovers must be eaten, be sure that it is within that three-day window, and be sure to reheat it on the stove, in the oven, or in the microwave until the internal temperature reaches 165 Fahrenheit. If you think you have a foodborne illness and your symptoms last more than three days, see a doctor or go to the hospital immediately. For more cooking tips or information, visit Gary Duff's newamericankitchen.com.