Have you ever spoken to someone about something and for some strange reason, you are able to tell when he/she starts getting confused/don't-have-any-idea-what-you-are-talking-about? Apart from the obvious confused look on their faces, and their stillness in their body language and/or pause in their activities, notice that they will also stare at you blankly. By this I mean they will stop blinking. Weird isn't it?
There are a lot of reasons why and when we blink but I think this one is quite interesting in it's own right and I'd like to talk a little about it. Seems blinking is also an activity linked with absorbing information. To me it's the nodding of the eyes. When you're listening to someone and you are in agreement, you tend to nod at them... and blink too! I know this seems odd, but try it for yourself. An example is when I am in a lecture hall and listening to a very informative and interesting lecture, I would catch myself blinking a lot. I mean a lot uncontrollably.
I believe the same is true when you stop agreeing. This is why it's quite shocking how we are able to tell when someone is lost while trying to explain something to them. It's easy to tell because we notice a change in behaviour or a break in a pattern. While the listener understands what you are talking about, they will often be blinking, nodding, etc and suddenly as they get confused, our brains are able to detect that change in behaviour, a different action performed out of the normal, even as subtle as fewer eye blinks. Try it and see for yourself!