To show the ‘photo-soap’ in action, the researchers used UV light to control the dripping of a capillary tube. The tube was filled with a solution of the new soap, and a tear-shaped droplet formed at the lower end. In the ‘open’ state, the soap has a relatively small effect on water’s surface tension, and so the droplet was able to cling to the end of the tube. But when subjected to a flash of UV light, the soap molecules took on their “V” shape and, after several seconds, made their way to the surface to lower the surface tension – with the result that the drip dropped. By the time the next drop had gathered, the soap had reverted to its ‘open’ state, and so the droplet hung there as before. In this way, Shin and Abbott could orchestrate the dripping of a whole row of tubes, conducting a raindrop prelude with flashes of light.