In the murky waters of the Amazon Basin, a fish glides effortlessly—forward, backward, and in place—without bending its body. The black ghost knifefish (Apteronotus albifrons) performs these feats using only a single, ribbon-like fin running along its underside. Now, a team of researchers has decoded the biomechanical principles behind this remarkable agility, offering a roadmap for building more capable and maneuverable underwater robots.