rehearsing the face you show other people
practice expressions, try to look all natural and uncomposed so you can try to see what you really might normally look like to other people.
Context
The empty locker room's best mirror is used for the theme's quiet daily labor: standing alone practicing expressions, trying to "look all natural and uncomposed" in order to glimpse "what you really might normally look like to other people." The self can only reach its own broadcast through a mirror and a rehearsal, composing uncomposedness — the gap between the inner man and his received image managed the only way it can be, by treating one's own face as a stranger's to be studied and staged.