Cameras mounted on earphones can monitor your facial expressions by the contours of your cheeks alone, which could be useful for importing facial expressions into virtual reality or lip reading
Source:
https://www.newscientist.com/article/2256925-earphone-cameras-watch-your-facial-expressions-and-read-your-lips/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home