 How well can you dance on a waterbed? Yes, sir. I don't think you can dance all that well on a waterbed at all. Why? Well... Because you sink. Every time you step, you sink, right? Well, it's not a solid surface that you're walking on. Exactly. So, now, this is a perfect example. You know the cells that are in your windpipe? Okay. They're called cilia. They are sitting on cells...