Squeeze a pipe and the fluid inside speeds up but pushes less hard
Force the same flow of air or water through a narrower section of pipe and its speed increases while its pressure drops, a phenomenon Italian physicist Giovanni Battista Venturi described in 1797. It's the same physics behind a perfume atomiser, a carburettor and a wine aerator. The effect sat as a scientific curiosity for almost a century before engineer Clemens Herschel turned it into a practical water flow meter in the late 1880s.