Fig. 2. Methods. Eels were filmed from below using two synchronized high-speed cameras aimed at a 45° mirror below the flow tank. A laser light sheet 7 mm above the bottom of the tank illuminated the eel's wake and part of its tail. One camera (labeled `kinematics') imaged the whole eel, and the other camera (labeled `PIV') imaged the light sheet. Representative images from each camera are shown to the left. Diagram is not to scale.