However, "Alice is able to notice" isn't a given. Yes, setting a hill on fire may be more likely to "get through" than sending a messenger in response, but the

However, "Alice is able to notice" isn't a given. Yes, setting a hill on fire may be more likely to "get through" than sending a messenger in response, but there's still a chance that the fire won't be seen. And, if no messengers (from Alice) got through, you might decide to set the hill on fire anyway, not knowing how Alice will interpret that act. Yes, better networks help, but as long as they're short of perfect....