What are you thinking?

This is totally trivial, y’all, but I’m curious. Most of us, I think, have had the experience of being asked “What are you thinking about?” and not being able to give an answer. We might say “nothing” or we might make something up. It’s frustrating to ask and get the “nothing” response, but it’s also frustrating to be asked. What I want to know is, when that happens, what are you actually thinking? Or what’s going on in your mind that makes it impossible to answer? I realized, for me, it’s nearly always the same thing, but I’m curious what it is for other folks.

I haven’t blocked repeat voters, so if more than one of these are common for you you can vote twice! If you put “other,” of course I’d love an explanation in the comments.