Why?
Plain unsalted olives are not toxic to dogs and contain some healthy fats and vitamins. However, most olives are preserved in brine making them very high in sodium.
How much can dogs have?
One plain unsalted olive occasionally is fine for a large dog.
What to watch out for
Most store-bought olives are extremely high in sodium. Pitted only — olive pits are a choking hazard. Stuffed olives may contain garlic or peppers which are toxic.