The physical properties of membrane necks are relevant in vesiculation, a 
process that plays an essential role in cellular physiology. Because the neck's 
radius is, in general, finite, membrane scission and the consequent pinching off 
of the vesicle can only occur if it is narrowed to permit the necessary membrane 
topological reformation. Here we examine, in a simple single phase lipid 
vesicle, how external forces can promote neck constriction not only by direct 
compression at the neck but also, counterintuitively, by dilation at remote 
locations. These results provide a new perspective on the role played by actin 
polymerization in the process of endocytosis.