It seems to me that there are two kinds of intrusive thoughts. The first consists of those thoughts that didn't actually occur in real life, but are nonetheless intrusive and embarrassing and disturbing to the individual (i.e. thoughts of harming someone else, or unwanted sexual thoughts directed towards individuals). The seconds consists of past memories of embarrassing moments, particularly from childhood.
I've noticed that many people will respond to these thoughts in some way. I've had many friends tell me that if I hear them 'talking gibberish' or 'making strange noises', it is because they are having a bad thought. I myself have noticed now that I will talk out loud when I remember an embarrassing thought -- but I won't speak of the thought, I will say random things, like "Okay, okay, okay" or "I love you". Usually, I will repeat a phrase over and over under my breath, until I catch myself doing it.
I've also noticed certain individuals will use verbal gestures to show that they are thinking of something negative. My father will scratch his head and blow out of his mouth for several minutes at a time when he is having intrusive thoughts, or 'conversations'.
Is there an explanation for this phenomena? Why is it that externalizing our thoughts seems to 'rid' our head of them?