Long, thin retraction fibers trail behind actively migrating bovine pulmonary artery endothelial cells. The strands of material are intermittently pulled away from the substratum and contract back into the cell to which they belong. A bout of heavy activity along the anterior margin of the cell usually attends the retraction of the fiber. Due to their generally broad leading margins and extremely narrow retraction fibers, the shape of some of the BPAE cells is similar to that of a stingray.

Oftentimes when BPAE cells come into contact with one another, the apparently rapid extension and contraction of lamellipodia known as ruffling that can be observed during the high speed playback of time-lapse sequences ceases in the area of overlap. Surface extension activity continues along other regions of the cells, however, which usually causes them to pull apart and migrate in different directions. Early in this time-lapse sequence, the BPAE cell tendency to initiate locomotion in a new direction whenever another cell impedes its initial path of travel is clearly demonstrated by a cell in the upper left side of the field of view. Finding itself surrounded, the endothelial cell seems to bounce about as if it were caught in a pinball game, quickly changing directions each time it comes into contact with another cell.

Although in the video the actions of the BPAE cells seem very brisk, it is important to remember that the 72 seconds viewed actually represents 24 hours of imaging. To a microscopist viewing the cells at any given moment during those 24 hours, the cells would seem almost completely inert. Indeed, early scientists studying cells had no notion of their complex motility. To obtain a better understanding of the full spectrum of motions carried out during a day in the life of cultured cells, high speed playback of time-lapse sequences is necessary.