And so there's really not too much energy that must be overcome as these phospholipids actually move along any given leaflet. But let's suppose, instead of moving along the lateral direction one of these phospholipids, let's say this one here wants to actually rotate and move from one side of the membrane from one leaflet to the other side of the membrane, that opposing leaflet. Will this actually take place. So this process is known as transverse diffusion, or simply flip flopping. So do fossil lipids actually flip flop? And the answer is yes.