Cells in close proximity to a solid surface, such as the bottom of a culture dish or imaging chamber, must overcome the viscosity of that substratum in order to locomote. To do so, a considerable amount of force must be generated. Close points of contact between the surface and the cell must be formed in order for the cell to be able to exert such a force. However, direct molecular connections between the substratum and the cell are not necessary because the viscous drag that develops from their close proximity supplies traction sufficient for cell locomotion.

Focal adhesions are specialized junctions between a cell and extracellular matrix molecules. At the focal adhesions formed between a substratum and an A. P. Mongoose cell or other fibroblast in culture, the plasma membrane of the cell is located roughly 15 nanometers away from the surface. 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 when the cell passes over them. As 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.

During the high speed playback of this time-lapse sequence, however, it can be readily observed that the linkages between a substratum and a cultured cell are not always easily broken. Several of the actively migrating mongoose skin fibroblasts lose small segments of their cellular material as they proceed along their chosen pathways. The fragmentation occurs because the cells are not able to successfully lift up all of their focal adhesions and must, therefore, leave some behind in order to advance any further. Notably, other fibroblasts may incorporate the debris of other cells into their own contents, as demonstrated by a number of the A. P. Mongoose fibroblasts.