Fig. 4. Three-dimensional positions of the head, midpoint, and vent in representative anchored and sliding J-loop take-offs. Head, midpoint and vent points are represented with triangles, circles and squares, respectively. Scale bar, 25 cm. Side (A), overhead (B) and rear (C) views of unsmoothed data sampled at 60 Hz. In both take-offs, the head traces approximately the same path, moving upward, outward, and then down. In the anchored J-loop take-off, the snake's head has a slight rearward component during the first upward movement. The upward movement during the initial acceleration has almost no lateral component. Note the relative lack of movement of the vent (gray arrow, A) early in the anchored J-loop take-off. Anchored J-loop take-off: mass=27 g, SVL=63 cm; sliding J-loop take-off: mass=26 g, SVL=62 cm.