Lasers may light the way to how respiratory viruses spread from person to person.

Scientists at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) found that people release thousands of saliva droplets per second when they’re talking. That’s important because those droplets, if infectious, could spread illnesses like COVID-19, the flu, or a cold.

Using a laser beam that crossed through the center of a very dark box, researchers were able to light up the droplets as people spoke into the box. They found that many of the smaller speech droplets could stay in the air for more than 10 minutes.

To see a video of the droplets, check out NIDDK’s YouTube page.