Penguins quite often, when they get out of the water have to get up, high up onto ice.
And the only way to do it is for them to swim upwards very, very fast and then as soon as they come out of the water, they have enough momentum to carry them up onto the ice shelf. 
The thing that makes that process more difficult is that hanging around on the surface are things like leopard seals which will eat any penguins that don't make this transition fast enough, so
there's an interesting evolutionary pressure on the penguins to get through that boundary as fast as possible, to be swimming as quickly as possible as they go up to the surface
so there are these very famous images in the Blue Planet of penguins swimming and they have always got these trails of bubbles. And everyone is just like, yeah "penguins have bubbles" and no one really thought about it
until a few years ago, at the University of Bangor, a couple of fluid dynamicists kind of went; "why is that? What's going on?".
So they had a bit of a think and it turns out that what the penguins do is really, really cool. The penguins, if you ever see penguins in the wild or on TV they are preening. They are constantly preening. The feathers are the most important thing the penguin has 
because they are its insulation and they are a large part of how hydrodynamic it is; how easy it swims in the water. 
So anyway, before the penguins go down to dive and they can be quite long dives, the penguins will fluff up their feathers and trap gas and trap bubbles underneath and then they go down and go hunting for fish and then it comes time to go back up to the surface and pop out onto the ice past the leopard seals.
So what they do is as they are starting that swim upwards, they sort of unfluff their feathers and they release bubbles, a coat of bubbles 
and what those bubbles are doing is inducing turbulence, just like the reason a golf ball has dimples, the bubbles are reducing the drag on the penguin and the penguin that is producing bubbles can travel 50% faster than a penguin that isn't.
So it stands a much better chance of getting past the leopard seals now onto the land. So, this is brilliant because it is this wonderful interaction of all sorts of different things. It is a physical process. The reason the bubbles come out is the penguin swims up, it is because the pressure is decreasing and the bubbles are expanding so they can come out of the feathers. They are reducing turbulence and drag, which is one of the most complicated problems in fluid dynamics and the penguins just do it.
And it helps them; it changes the ecosystem because the penguins can survive in conditions they would not otherwise be able to survive in. So penguins use bubbles and I think that's brilliant!
