Sakai et al. reported on the role of NA in the surface motilityof influenza.4,5 De Haan et al. found that virusescleave receptors in a large area around them and proposed that virusesroll over cell surfaces.6 Vahey and Fletcherfound evidence of directional motion by influenza,1 while Müller et al. showed that the mobility ofinfluenza relies on a delicate balance between binding and cleavingof receptors.7 The surface motility ofinfluenza may assist in finding or forming clathrin-coated pits. The gene discussed is XK; the disease is influenza.