Penguins
I had the chance to see lot of penguins during two campaigns in Antarctica.
Their ability to displace in the water is incredible. When moving quite fast, one or two meters below the surface, they make 90º turns effortlessly, but when it comes to walk on the beach, they are incredibly limited to the point they cannot run at all. That is why we call them "pájaro bobo" (silly bird).
If you chase them, they will fall and have to crawl until reaching the water.
Once, when passing with our vessel along an ice field, I saw maybe 10 or 15 penguins standing on the edge of an small tabular piece of ice and a seal on the water making turns in front of them.
They were all moving continuously to the sides against its neighbours, obviously trying to make one of them to fall into the water. Finally one did. Since the group was falling behind, it became out of sight.
I couldn't see what the seal did.
But sure, I can guess.