Pet Poison Helpline receives a spike in calls and lists the following as fall carnival or Halloween pet hazards:
CHOCOLATE: Methylxanthines in chocolate cause signs of toxicity from vomiting to seizures. Baker's chocolate is more toxic than milk chocolate however pets should be kept away from all types.
SWEET CANDY AND FOOD: Pancreatitis can result from excess intake, and especially avoid candy with xylitol used as a sweetener as it can result in liver damage and low blood sugar.
RAISINS: Relatively small amounts of raisins and grapes can cause kidney failure and pets should be prevented from eating these, especially if they are coated in Chocolate!
CANDY WRAPPERS, COSTUMES AND CANDLES: all create hazards either from ingestion of buttons or strings or from burns. Make sure to secure these away from pets; if your pet has a costume watch out for zinc or lead parts as well as parts your pet can swallow.