Fig. 2. Limb movement and force generation. The heel of the raptorial appendage (purple, right y axis) approaches the force sensor (located at distance 0, right y axis) and generates force (black, left y axis) during impact (peak 1) and when cavitation bubbles collapse (peak 2). Negative pressure as the limb rebounds from the sensor surface is indicated by the slight negative excursion of the force trace between the first and second force peaks. Distance data was digitized from high-speed video (100,000 frames s^-1) and smoothed using the negative exponential function (polynomial regression and Gaussian density function; SigmaPlot v.9.0, Systat). The one-axis force sensor was sampled simultaneously at 100,000 samples s^-1.