What is it that flags us that a person hasn't seen you and is about to run the stop sign, or that the person in front of you is getting ready to change lanes before they use their blinker?

Today I came upon an intersection, and the intersecting street had a stop sign. I didn’t. This lady sorta kinda stopped, and the way she was looking blankly around told me that she flat did not see me. I don’t know how she could have missed me because I was in a giant assed black SUV (it’s the only vehicle we have at the moment. Working on that,) but I could just tell that she didn’t and she was going to flat run right into the side of my truck. I came to a full stop after I started to enter the intersection. It was rather aggressive, but I wanted her to understand that I had the right of way and I was going to take it. Stopping outside of the intersection could have been interpreted as me creating a 4 way stop and wouldn’t have made my point at all. Sure as hell she started to pull out, right in front of me, inches from my bumper, then did this “Where did you come from!” startle thing, and stopped.

I also kind of get a sense when a car in front of me on the highway, is going to be turning soon, or going to change lanes, if we’re on a 4 lane before they ever use their blinker.

Do you do this too? What clues are we picking up on?