What causes random thoughts and remarks?

"Random" is only a perception. As relates to thoughts, no thoughts are truly random. Humans think in a connective way. That is our thoughts are driven by other thoughts, things we see, or things we experience. Each even can trigger thoughts or a series of thoughts. Think of it this way. What was the name of your first grade teacher? You may remember or you may not. But, you were not thinking about your first grade teacher until I mentioned it. Now, as a result of my question, you may now be remembering events that occurred while you were in first grade. You might even recall your teacher's name. This is not random. Rather, it is a direct result of something I did.

Remarks are another matter, but no more random. Unless you suffer from a condition similar to Tourette's syndrome, you have total control over the remarks and sounds you produce. You simply choose to say what you say it when you say it. Your reasons are your own.