What if it turned out they already do?
[T]he muscles of the face make constant tiny movements [...] much like the tiny movements the eye makes to stay focused on something. But while the patterns traced by the eye form only a random etch-a-sketch of squiggles and curves, the motions of the lips [...] are effectively the same as those made during [conscious] speech.
The monologs rarely form complete sentences even at their most lucid. The most coherent "speech" occurred when subjects were observing a partner in a shared activity. [...]
4 One subject's lingual saccades had consistent themes of violence. While working together with a researcher on a task in which plastic gears were connected together, his internal monolog contained statements such as "think of all the lives I could be taking instead of dealing with THIS idiot."