A strange sound rises from the cinnamon-coloured sand: a deep, almost hypnotic rhythm. It could almost be the chanting of Tibetan monks, a song beyond time, yet the setting is rigorous and clinical -- the laboratory of French physicist Stephane Douady, where a robot arm is pushing small, precisely measured amounts of sand down a plexiglass ring. Douady is a leading expert in a very narrow field. He is investigating one of the most romantic yet maddening phenomena in the natural world: the "song of the dunes." The noise occurs when the ridge of a sand dune builds up and eventually topples. This shear effect causes a mini-avalanche of sand in which millions of grains rub against each other as they fall. But different materials and different conditions make different songs, says Douady.