Two scientists recently hit the headlines when they created mutant strains of H5N1 influenza, which can spread between mammals. Their experiments began when they tweaked the H5N1 virus to reproduce in a ferret’s airway. Then they introduced random alterations into the haemagglutinin (HA) protein, which the virus uses to stick to host cells. From the resulting library of mutants, the researchers isolated viruses with two mutations in HA — N224K and Q226L — which allowed the virus to stick to receptors in human tracheal cells. That is something H5N1 viruses cannot usually do.