What @augustlan said, pretty much. A constant internal dialogue that just rambles on about what it was already rambling about, whether I brush my teeth or not.
If you want a concrete example, it could be along these lines.
“I wonder if flies will ever evolve to understand you can’t fly through a closed window, no matter how hard you try. I guess windows don’t exist long enough yet to expect that sort of thing. Wait, how long does one fly generation take anyway? Viruses have evolved within documented history. I think those are simpler evolutions, though. I wonder how many generations you would need to build an instinct to stop trying when the glass won’t budge. Or maybe to take away the instinct that light equals a place you can fly through. But that would probably get them into trouble with other things. I guess you’d need to ask a… who are about instincts again? Behavioural biologists, or something? Those people who make rats push buttons to get food. I read about them just a few days ago. Is there a name for that, anyway, or is it just another kind of biology? Then again, even sub-fields within larger fields have names of their own. I’m pretty sure it should be something with “behariourism” in it. I could probably look up Pavlov on Wikipedia to find that term again…”
Et cetera.