Here's why:
* Cytokinesis: Cell division in animal cells involves two main stages: mitosis (nuclear division) and cytokinesis (cytoplasm division).
* Cleavage Furrow: During cytokinesis, a contractile ring made of actin filaments and myosin proteins forms just beneath the cell membrane. This ring contracts, pinching the cell membrane inward and creating a furrow that gradually deepens.
* Final Division: The cleavage furrow continues to constrict until it completely separates the two daughter cells.
This process is distinct from plant cells, which form a cell plate during cytokinesis.