The strap gets fixed after she notices him looking. That is the part he cannot unsee.

She had a mirror. She had the black car window outside. She had the bathroom with the buzzing light over the sink. Still, the little correction happens right there. Thumb under the fabric. Hair pulled off one shoulder. Jacket opened, then closed again, as if the room suddenly changed temperature.

It usually comes with an annoyed face, which is almost better cover than a smile. A small frown says, don’t look at me. The hands say something less clean.