Could sniffer dogs be a response to congested Covid-19 test programs? Researchers at the Alfort National Veterinary School near Paris have trained a group of dogs to detect Covid-19 in samples of human sweat taken from hospital patients. The system is already in use in Australia, Argentina, Lebanon and the United Arab Emirates, but it has not yet received a clear signal from the French government. Make sure that the dogs are not exposed to any injury or danger. Claire Paccalin and Eleonore Vanel report.