Movie 2.

Description: swimming trial of Natrix F1 during the PIV experiment. The video captures the snake's swimming motion from the side using the top PIV camera. Simultaneously, the PIV measuring volume is depicted, showcasing isosurfaces of the Q-criterion. These isosurfaces are colored based on the vorticity around the X-axis, effectively highlighting the resulting vortices. The video then shows the created tilted plane, collinear to the vortex trajectory, were the local vortex size (d) and circulation (Γ) are measured.