While pouring the hot water onto the [herb] leaves, Ernesto Althsuler and buddies at the University of Havana in Cuba, noticed a puzzling phenomenon. They found that, sometimes, the leaves would somehow travel upstream and end up contaminating the upstream container of pure water.Details at the link. It has potential implications for "chemical, medical, pharmaceutical and industrial processes."
Being diligent physicists, they decided to investigate. They found that the leaves (and also chalk powder) were able to navigate upstream if the waterfall was less than about a centimetre in height. "For distances of the order of 1 cm or less, some of the floating particles eventually start to "climb up the stream"," they say.
Via Swans on Tea.