Have you ever tried to count how many levels of thoughts you have? I used to do it all the time when I was little..probably every day. I think it's impossible to count them all. There's the first level which is like talking inside your head- your most prominent thoughts.  Then there's that level that's thinking about what your first level is saying. Then the next level is thinking about everything all together and trying to analyze it...and so on.  I think the most I can count is 3 or 4.  It keeps you occupied for a long time. Try it during long block.

Here's another: Try listening to someone talk and don't focus on any of the words- only sounds. But do it consciously.  It's so hard to not process the words.  If you do manage to do it, you realize that english is a really ugly language. We have so many gross sounding words.