"[T]here are these very famous images in ' of s swimming, and they've always got these trailing bubbles. ...[N]o one really thought about it until a few years ago at the University of Bangor, a couple of fluid dynamicists... had a bit of think, and it turns out that what the penguins do is really... cool! ...They are constantly preening. The feathers are the most important thing a penguin has because they are its insulation and they are a large part of how hydrodynamic it is. How easy it swims through the water. ...Before the penguin goes down to dive, and they can be quite long dives, the penguins all fluff up their feathers and trap gas... bubbles underneath."