Some people sometimes talk to themselves. That does not necessarily mean they are mad or mentally ill. But, interestingly, people don't do that in front of other people, they do that when they think nobody is around, because talking to oneself is considered a sign of madness!
Anyway, the other day I was walking in the street and saw this guy talking to himself; he was ....
What verb should I put in the blank to mean talking to himself?
I just like to maintain that I am looking for a "verb", and that I am aware of the nouns for that kind of action, nouns such as "monologue" and "soliloquy". And, anyway, these two examples seem to mean rather long talking to oneself as in movies and theater, and thus they might not be good nouns for talking to oneself in the street, because such talking might consist in just one single sentence.