Robot squid that move to a rhythm can match the power efficiency of the real animals, a trick that could be useful for designing next-generation submarines. Real squid have small fins that they use for careful manoeuvring, but when a big burst of speed is required they suck in and expel water to propel themselves. Researchers have tried to build robots that mimic this jet-like behaviour, but now a team led by Gabriel Weymouth at the University of Southampton, UK, has discovered a way to boost their efficiency. Weymouth and his colleagues created an umbrella-like robot with eight 3D-printed plastic ribs covered by a rubber skirt. It flexes outwards to suck in water and contracts to expel it, providing thrust.