Boundary motion can be analyzed as a series of discrete protrusive and retractive events or as continuous movement.

<p>(A) In this plot of the evolution of local boundary motion, protrusive motion appears red, while retractive motion appears blue (<i><a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002392#pcbi.1002392.s015" target="_blank">video S9</a></i>). (B) Extracted individual protrusions are shown as black dots, while extracted retractions are shown as white dots. (C) The averaged location of protrusive and retractive motion, which is defined in each frame where boundary motion is above a noise threshold, are shown here. This cell is also shown in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1002392#pcbi-1002392-g001" target="_blank"><i>figure 1</i></a>. (D) The mean squared displacement of the mean protrusive location is ballistic on short time-scales. The black lines, from left to right, have slopes of 2, 1 and 0 micrometers/min.