And although they are weak compared to the covalent bonds that actually hold the atoms in any one of these molecules. The collective aggregate of older forces make the membrane an effective barrier. Or property number five is the membrane is not rigid, it is not stationary, it is fluidlike. And that's because of these relatively weak non covalent interactions. So basically, these proteins and these phospholipids, the lipid molecules, can move along the membrane without any problem. So there's a constant state of motion among all these different molecules in the lateral direction on that cell membrane.