Speech Impediments

Have you ever met someone who responded to what you or other people said before they finished saying it?
Everyone does at some point. Children instinctively know when their mother is leading up to the fact that their homework is unfinished. Couples finish each other’s mushy, googly-eyed sentences. Certain topics just have typical and obvious conclusions that let us all chime in at the end.
But what about when there is no way of knowing what the person will say?
The speaker begins by saying that he/she recieved a call. There is no way of knowing what this call is about, but immediately the interupter cries out, “Oh dear!” Phone calls can be good, they often are. What prompts this person to make an exclamation before the opening statement is even finsihed?
Another time someone may begin by saying that a friend came to see them. The interupter make a sound of surprise. Why shouldn’t the friend have come to see speaker? At this juncture no one knows who the friend is. I think the interupter probably wants to be perceptive. The interupter thinks that he/she can sense the direction something is going. This only work if the interupter does not consistantly, as if by some social instinct in reverse, give the wrong answer. The call was good, the friend is welcome.
Is it ever kosher to walk up to someone and say, “You might wait till people finish their sentences every once in a while. You know, just to see what happens.” ?