In the young discipline of robotics-inspired biology, robots replace experimental animals, allowing researchers to learn about animals under a wider range of conditions than exist in nature or the laboratory. What is the secret behind the steady but oh-so-elegant way in which cats move? That's the subject of a study in Frontiers in Neurorobotics by scientists from Osaka University, who built a novel, 47cm-long and 7.6kg-heavy robotic cat. Based on previous research on the gait of real domestic cats, the authors deduced that key to the cats' sleek movement must lie in a previously unknown reflex circuit, which they call the "reciprocal excitatory circuit between hip and knee extensors". According to their hypothesis, this reflex circuit has two essential features.