A police officer places a sweat sample for a sniffer dog to detect COVID-19 at Lebanon's Rafiq Hariri International Airport in Beirut on March 1, 2021. - Specifically trained sniffer dogs can detect Covid in a person in a few seconds, including in very early stages when a PCR test would yield a negative result. Each dog can process hundreds of samples every day, the only wages they need are biscuits or rubber toys and they deliver results on the spot. (Photo by JOSEPH EID / AFP)