Every tissue of our human body consists on cells and cells are not like static "LEGO bricks". They are highly dynamic and can actively move around, due to myosin-actin networks inside the cell that are fueled by the hydrolyzation of ATP. However, most of the tissue is attached tightly in place. Clearly there is cell migration e.g. in case of wound healing.
But is it possible that tissue flows apart from the body due to the active nature of cells? Under which circumstances this can happen?
Blood is considered a specialized form of connective tissue and it can flow.
Early in embryogenesis, there are motions which do not flow apart from the embryo, but flow within it in order to shape it.
See e.g. this movie Drosophila embryogenesis
These collective motion are not migration (they don't rely on propelling cells with respect to a substrate) but rather a flow (since there is a change of neighbourhood relations between cells, which is a characteristic of liquid-like flow compared to solid-like deformation), see that other movie at cell scale
Actomyosin is also a crucial player in those movements. The fact that extra-cellular matrix is not yet existent or only nascent during most of these movements is believed to be a key reason why these movements can be much more liquid-like than most deformations in later development.
