We perceive the world selectively and rely on our expectations. We are accustomed to a life of ever repeating experiences. This waterfall which flows upwards breaks this intuition and brings our perception of reality into question. 

The illusion is realised using a stroboscope which is tuned to a slightly different frequency relative to a series of loudspeakers. Single water droplets fall out of nozzles attached to the loudspeakers and seem to be flowing upwards in the light of the stroboscope.