In fluid dynamics, the tea leaf paradox is a phenomenon where tea leaves in a cup of tea migrate to the center and bottom of the cup after being stirred rather than being forced to the edges of the cup, as would be expected in a spiral centrifuge.
Visualization of secondary flow in river bend model (A.Ya.Milovich, 1913, flow from right to left). Near-bottom streamlines are marked with dye injected by a pipette.