And that's exactly why they do not actually flip flop. So we conclude three important points. Point number one, phospholipids move relatively freely and quickly along the lateral direction. And although proteins can also move relatively quickly along the lateral direction, some proteins are actually immobilized because of attachments to other structures. Now, although these phospholipids can actually move transversely, they can flip flop. The rate at which they flip flop actually takes place at a much lower rate than lateral diffusion.