Losing the ability to smell is one of the strangest clues that someone may have COVID-19. Experts around the world are still trying to understand why this symptom pops up, and what it means for patients. Some are calling on people who have lost their sense of smell to get tested and isolate themselves, even if they have no other symptoms. Jason Gale reports that the symptom could be an early warning sign--and screening for it could help contain the virus.6