No, I suppose that one accidentally eating a piece of a kaner (oleander) fruit is not very likely to kill. Yet, it is a very poisonous plant and any of its parts will cause very severe symptoms e.g. vomiting, diarrhea, abnormal heartbeat, or even death. If you or somebody associated with you accidentally partakes in the substance of the plant kaner, then first aid treatment is a must. Please see a gastroenterologist or go to the emergency room as early as possible.