Fig. 3. Overhead view of snake's landmarks during aerial undulation. Points represent the head/body junction (triangles), body midpoint (circles) and vent (squares) from one snake during one trajectory, sampled at 60 Hz. Temporal sequence is from bottom to top. As the snake moves forward along the trajectory, traveling waves move posteriorly down the snake, producing a side-to-side undulatory pattern in which the head and vent move out of phase with the midpoint. At the beginning of the sequence shown, the head is moving to the left relative to the midpoint. The frequency of undulation and maximum wave height (approximately the distance between the paired black arrows) were 1.3 Hz and 24% SVL, respectively, with an average airspeed of 6 m s^-1. Scale bar, 20 cm.