Crayfish fluid flow experiment. Experiment showing a jet of coloured water (left) created by a red swamp crayfish (Procambarus clarkii). The crayfish, viewed head-on, is suspended within an aquarium by a holder (top, centre) and placed on a treadmill. A tube (lower left to lower centre) pumps ink towards the head of the crayfish to reveal fluid flow. This species normally inhabits stagnant water and creates jets using specialised pumping and fanning appendages to allow water to flow towards its chemoreceptors and detect odours. The jets can be directed at varying angles. It is thought that the mechanism allows the crayfish to remain stationary and reduce the risk of predation. Photographed by Petr Denissenko, Fluid Dynamics Laboratory, University of Hull, UK.