Video 2

Movie S2. Synchronization of a pair of wild-type animals swimming in a conduit. (Top) Two nematodes inserted in a tapered conduit swim toward the narrow end of the conduit against adverse flow (∼100 s⋅µl/h) and in the presence of a weak direct current (DC) electric field (4 V/cm). The initially trailing animal eventually passes the leader. The video plays in real time. (Bottom) An animation showing the level of synchronization (S) as a function of the normalized distance between the two animals. The small green dots correspond to individual data points, the large red crosses and error bars correspond to the average synchronization (S¯) and the SD of S as functions, respectively, of the normalized distance between the animals D1D. The blue disk-shaped marker indicates the approximate relative distance between the two animals in the video played above.