We rely on our intuition more than we realise. How often do we stop to question if what we just witnessed really did happen? It could have just as well been an illusion or a misunderstanding.
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.