A mouse-like robot with an articulated spine is faster, more agile and defter at balancing than rigid competitors, but the added cost and complexity means such devices will only be suitable for some applications. Zhenshan Bing at the Technical University of Munich, Germany, and his colleagues created their robot using a 3D printer. Its flexible spine has eight joints controlled by servos, and the whole machine is about 40 centimetres long and weighs 225 grams. The team put the robot through a variety of tests with its spine rigidly locked, and then again while allowed to use its full range of movement. A balance test that involved lifting each leg in turn tipped the robot over with a rigid spine, but in the flexible test, it was able to change its centre of gravity by bowing its spine and remain upright.