Your hand entering the bag is just to simulate the mechanical forces within the cell - if you look at this image (<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Endocytosis#&#x2F;media&#x2F;File:Endocytosis_types.svg" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Endocytosis#&#x2F;media&#x2F;File:Endocy...</a>) it might help to visualize the mechanism in question.