Rolling produces regularly periodic changes in orientation for hyperactivated sperm. (A) Tracking the head centroid of a free-swimming hyperactivated sperm. Duration 2 s, sampling 100 frames per second (fps), medium HS. Heavy red and blue lines indicate right cheek (RCh) or left cheek (LCh) orientation during the initial 1 s. Arrows indicate location of the stop-motion images below. (B) Intensity of light from a 7 ± 7 pixel region of interest enclosing the centroid (black) also follows a sinusoidal path (green) that peaks near transitions between RCh and LCh orientations. (C) Aligned waveform traces sampled at 50 fps during the initial approximately 0.5 s of tracking. Initial trace is green; final trace is purple. Red and blue indicate cell orientation. (D) Flagellar asymmetry reported by the time-averaged tangent angle (shear angle).