I start thinking they find me frightening and wonder what I did wrong. But I read body language well enough that most people give me some signal as to what's happening in their heads....quite often more than they might like, I think.
Yes, I assume they are not interested in my story and I cut it short. My friend does this a lot and I just don't bother - I stop the conversation and move on. She says it's because she is always "very quiet". I think it is because she cannot relate to what is going on. I don't like talking to walls.
Yes. Poking at them with a pointy stick makes a huge difference though
Yes. If the person has a completely blank face, is entirely still, and does not show any nonverbal social cues whatsoever, I feel extremely uncomfortable and will feel myself drift away from that person. I will want to avoid him/her because something about my interactions with that person causes me to feel uncomfortable and unappreciated. I need something that communicates warmth - like a thoughtful "mmhmm" or a headnod or even just "open" body language - not sitting stiff and cold... I honestly can't stand having conversations with people that do not communicate feelings. I don't feel like I'm interacting with a person.