I'm not actually sure what's going on in that video. It could be that the cells on the top are sinking or floating out of focus of the microscope.
You can shrink cells under a microscope too. By putting them in salt water. This will cause them to lose water and shrink.
This is better seen with plant cells, like onion cells because they have a cell wall around the membrane that keeps the cells in place and easy to view.
In the video below first the cells are exposed to salt water. Then distilled water