At this point, if I get confused or feel like I'm getting mixed signals a lot of the time I cut through the crap and just ask: "Do you want to continue talking about this or should we talk about something else?" I say it in a very friendly, non confrontational and pleasant manner, sometimes add something like "because I feel like I'm boring you/I'm not emotionally attached to this subject/I want to keep talking but I feel like you might want to move on to something else/WHATEVER"

At that point the ball is in their court. If someone has a problem with me directly addressing what I feel I'm picking up, I'm just not sure how to deal with that. Because then that is probably a person who just has no idea what they want OR there is just no pleasing them, and then you should probably move on to someone who would like to attempt to be a reasonable human being.

I propose it ISN'T always obvious why a person is presenting the way they are. There are a million reasons why someone might seem they are bored: maybe they are confused and don't want to seem stupid, maybe they are actually tired and don't have the energy to give complex responses but actually want to hear more, maybe they are distracted, maybe they want to BE distracted... hey, maybe they are actually bored.

You don't know if you don't ask.
You don't ask, you could miss out on something.

[of course if I'm feeling crazy at the time, all bets are off!]