What features of Penguins make them different from other birds?

Penguins are birds and they cannot fly. The one cool thing about penguins are that they can swim in cold water and they eat fish and not worms like other birds. Every bird has a special quality or something that is "cool" about them. And penguins cannot fly but they swim.

Penguins are aqua-dynamic, not aero-dynamic, like most other birds.