Play the movie through to the end and examine the late stages first, so you can see the tissues that are forming. We see a single plane of focus, and the mesoderm layer is in focus in the center of the field. You can easily recognize the notochord rudiment in the center of the field, 2-3 cells wide at the end of the movie. Two somite furrows also become visible in the mesoderm to either side of the notochord. Identify dividing cells in the movie to verify for yourself that divisions are asynchronous during the gastrula period of development.
Cells intercalate to drive convergence and extension, like they do to drive epiboly.
Stripe MooV shows dramatically, in cartoon form, the cell rearrangements during convergence and extension. Those developing somitic mesoderm are red, and those developing notochord are green. The cells in the germ layers are rearranged again, into the organ primordia during this third phase of embryonic development. We only get the barest hint of the goings on from the Zebrafish flipbook MooV. Observe the somites pinching off in an AP series. With the chick sections we can make good use of the fact that development happens in such an anterior-posterior wave, as explained in the lab write up.