What properties does second sight have and what makes it such a source of social anxiety?
I can answer the first part to a degree but have more difficult with the second. Look at a further avoidance strategy. My introduction to the subject, aged about 6 or 7.
Returned home from playing while visiting my great aunts house. She was bent over, mumbling and doing something to the right corner of the bottom of the door.
What are you doing?
She stood up and explained that she was covering the four corners of the door with holy water. Her next door neighbour was ill and that she was concerned that my great-uncle Pat would see a banshee.
She appeared to be working blind, she could predict that a banshee may appear as she had knowledge of the type of environment attractive to such creatures i.e. the landscape the Banshee walks through is one close to death. Degree of uncertainty, this is not an exact science.
Certainty here is going to depend on visual perception and that form of vision is more problematic for my uncle than my aunt.
What clearly has to be avoided at all cost is the vision of such a thing. Other factors at play are not entirely clear to me yet. Is sight restricted to one person here or is the social cost just higher for one gender?
What exactly is it that people are so keen to avoid here? It seems to be far more than simply a premonition that Mrs Macpherson next door may soon die.
What ever it is, its anxious, emotional, not something clearly expressed. The fate of such things would appear to be hedged with considerable uncertainty.