  We exploit the reduced space of C. elegans postures to develop a novel
tracking algorithm which captures both simple shapes and also self-occluding
coils, an important, yet unexplored, component of worm behavior. We apply our
algorithm to show that visually complex, coiled sequences are a superposition
of two simpler patterns: the body wave dynamics and a head-curvature pulse. We
demonstrate the precise coiled dynamics of an escape response and uncover new
behaviors in spontaneous, large amplitude coils; deep reorientations occur
through classical Omega-shaped postures and also through larger, new postural
excitations which we label here as delta-turns. We find that omega and delta
turns occur independently, the serpentine analog of a random left-right step,
suggesting a distinct triggering mechanism. We also show that omega and delta
turns display approximately equal rates and adapt to food-free conditions on a
similar timescale, a simple strategy to avoid navigational bias.
