Princeton’s Howard Stone and Manouk Abkarian, a research director at the French National Centre for Scientific Research, have directly visualized how speech and breath produce and expel droplets of saliva into the air. The smallest droplets can be inhaled by other people and are a primary way that respiratory infections like COVID-19 spread from person to person. https://www.princeton.edu/news/2020/10/12/how-exactly-do-we-spread-droplets-we-talk-engineers-found-out%20