To survive and fulfill their biological functions, cells need to take in material from their environment. In this process, proteins within the cell pull inward on its membrane, forming a pit that eventually encapsulates the material in a bubble called a vesicle. Researchers from the University of Pennsylvania have now revealed a relationship that governs this process, known as endocytosis. To get around the limitations in what they could see through their microscopes, the developed model cell membranes. The membranes, labeled red, were partially sucked into a pipette. Membrane-bending proteins, labeled green, pulled the membrane out during endocytosis. By measuring the amount of membrane left in the pipette, they could track the relationship between cell tension and the amount of membrane-bending proteins at work.