CAGED IN A GRANULAR FLOW In normal fluids, microscopic fluctuations are associated with an internal temperature, unrelated to the mean flow. According to Boltzmann's kinetic theory, collisions cause molecular positions to switch from ballistic (linear) to diffusive (square root) scaling in time. Kinetic theories have also been proposed for dilute granular flows, taking into account inelastic collisions via a modified "granular temperature". The new experiments of Choi et al., however, reveal a radically different, non-thermal picture of dense granular flows. By tracking grains with high resolution in a draining silo at different flow rates, the authors find a universal transition from (sub-ballistic) superdiffusion to diffusion, as a function of distance dropped, not time. In other words, the system seems to go through the same configurations, only more slowly, with decreasing flow rate. The cage breaking distance is also shown to be very long, comparable to the system size, showing that grains tend to remain stuck with their neighbors. These observations call for new statistical theory based on cooperative rearrangements, not collisions.