public static void AddCreatureKilledInvoker(ObstacleController creatureKilledInvoker)
{
// add the new invoker to the list of invokers
creatureKilledInvokers.Add(creatureKilledInvoker);
// ensure that all existing listeners are added to this new invoker
foreach (UnityAction <string> listener in creatureKilledListeners)
{
creatureKilledInvoker.AddCreatureKilledListener(listener);
}
}