… To themselves, I mean, whether they sounded neurotypical or not.
For instance, I learned this one guy likes the Navy/Marines, laughs a lot, knows the chorus to “I Am Your Lady” (as far as I can tell), and that his one big dream is to have two dogs and a truck and go fishing up and down the Oregon coast.
Talking out loud . . . in their sleep?
No, just talking. Either to themselves or nothing.
I can’t think of anything I have learned that way… however, if the pretty ladies I see whilst driving could hear me say, “holy fuck”, or “yowsa” or “wow…” to myself then they would know that I was digging them.
Thank goodness for all involved that they can’t but they would learn that tidbit of useless info 
“Titties are never free.”
Heard on Bourbon Street a few weeks ago when a strip club barker tried to get some young frat guys to come in to see some “Free Titties”. The above quote was their reply to him.
I learned that the guy on the other side of that one hotel room door was masturbating like a motherfuck.
I learned that the bag lady resting in the library should have killed the son of a bitch when she had the chance.