Northwestern University professor Malcolm MacIver’s GhostBot is a robotic fish that can swim forward, backward, and vertically using its incredible ribbon-like fin. Ghostbot’s locomotion is inspired by a knifefish in MacIver’s aquarium, which a colleague observed making an unexpected, vertical movement.

Further observations revealed that while the fish only uses one traveling wave along the fin during horizontal motion (forward or backward depending on the direction on the wave), while moving vertically it uses two waves. One of these moves from head to tail, and the other moves tail to head. The two waves collide and stop at the center of the fin.

[via Neatorama]