The lamprey's body is gray, and the areas where muscle is active are shown with black lines. Note that the active muscle moves backwards slightly faster than the fish moves forward, which is typical of fish swimming. Water movement is shown with red and blue colors, where red represents a vortex that is rotating clockwise and blue is a vortex rotating counter-clockwise. The swimming speed is shown in the graph at the bottom, with an open circle corresponding to the frame in the movie at the top. The small fluctuations in speed are caused by the rhythmic shedding of vortices.