Counterclockwise swirls in between cells confined in a thin film near surface

This real-time movie shows a microbubble tracer making 12 full circles counterclockwise (CCW) in 13.35 s, ~0.9 revolutions per second. This CCW swirling is a result of CW flows around individual cells. See: Wu et al., PNAS 108(10): 4147-51.