The study by Katz et al. investigates the structure and dynamics of interactions in schooling fish, specifically golden shiners (Notemigonus crysoleucas). The researchers analyzed trajectories of fish swimming in two- and three-fish shoals to map the mean effective forces as a function of fish positions and velocities. They found that speed regulation is a dominant component of how fish interact, with changes in speed transmitted to both those behind and ahead. Alignment emerges from attraction and repulsion, and fish tend to copy directional changes made by those ahead. No evidence was found for explicit matching of body orientation. By comparing data from two- and three-fish shoals, the authors challenge the standard assumption that individual motion results from averaging responses to each neighbor, showing that three-body interactions significantly contribute to fish dynamics. Pairwise interactions, however, qualitatively capture the correct spatial interaction structure in small groups, which persists in larger groups of 10 and 30 fish. The findings suggest that the interactions revealed may help account for the rapid changes in speed and direction that enable real animal groups to stay cohesive and amplify important social information.The study by Katz et al. investigates the structure and dynamics of interactions in schooling fish, specifically golden shiners (Notemigonus crysoleucas). The researchers analyzed trajectories of fish swimming in two- and three-fish shoals to map the mean effective forces as a function of fish positions and velocities. They found that speed regulation is a dominant component of how fish interact, with changes in speed transmitted to both those behind and ahead. Alignment emerges from attraction and repulsion, and fish tend to copy directional changes made by those ahead. No evidence was found for explicit matching of body orientation. By comparing data from two- and three-fish shoals, the authors challenge the standard assumption that individual motion results from averaging responses to each neighbor, showing that three-body interactions significantly contribute to fish dynamics. Pairwise interactions, however, qualitatively capture the correct spatial interaction structure in small groups, which persists in larger groups of 10 and 30 fish. The findings suggest that the interactions revealed may help account for the rapid changes in speed and direction that enable real animal groups to stay cohesive and amplify important social information.