If you sing indoors without a face mask, you run the risk of spreading COVID-19 through tiny airborne particles known as aerosols. That's the conclusion researchers reached after studying a choir practice. In Skagit Valley, Wash., one person with mild symptoms of COVID-19 attended a 2.5-hour-long indoor choir practice on March 10. Over the next several weeks, more than 50 others from the rehearsal got sick and two died.