Focal adhesions are specialized junctions between a cell and extracellular matrix molecules. Each junction represents an attachment site of a stress fiber, which is composed of bundled actin filaments with anchorage proteins positioned at the terminating end. Focal adhesions predominantly form along the leading margin of a migrating cell and act as anchorage points as the cell passes over them. When the cell advances and previously formed adhesions become distal from the leading edge, the junctions are usually released and the material located at the site of adhesion is retracted into the cell.

Early during this digital video, however, a PL 1 Ut cell locomoting across the top of the field of view appears to lose many small segments of cytoplasm. The cell fragments are produced when focal adhesions between the fibroblast and the substratum are not properly released, forcing the cell to take the draconian measure of severing pieces of its own cytoplasmic material in order to continue unhindered along its path. When the lamellipodia of other migrating cells pass over the material, they sweep up the fragments and incorporate them into their own cellular contents.

Along the leading edge of each freely migrating raccoon fibroblast, prominent ruffling occurs as lamellipodia are repeatedly drawn up from the culture medium and move toward the rear of the cell, eventually collapsing like waves breaking on a shore. The continual activity of the surface protrusions can produce a flickering sensation during the high speed playback of time-lapse sequences. Ruffling can occur in several locations simultaneously along the periphery of a cell, but ceases in areas of overlap between neighboring cells.