Underwater, Antarctica's Weddell seals are fast-moving, graceful predators, catching and eating as much as 100 pounds of food per day. They dine on squids and fish and have been known to enjoy the occasional penguin or two.
On land, they are hilariously ineffectual blobs of jelly.
You can see that dichotomy in action in this great (and long) video made by Henry Kaiser in Antarctica. Following the adventures of a baby seal on the ice and under the water, the video is peaceful, meditative and reminds me a bit of the sort of old-school Sesame Street video that would build simple, kid-friendly narratives out of nature footage and music. (The music, by the way, was written and performed by Henry Kaiser, as well.)
Despite their poor performance in land-based locomotion, Weddell seals actually live on the ice, descending into the water to hunt and mate and swim around. They use natural holes in the ice to get from above to below and back, but they also work to maintain those holes and often use their teeth to chew at the edge of the ice and make a small hole larger. At about 13 minutes into the video, you can watch a seal doing just that — rubbing its head back and forth to enlarge an opening in the ice.
And why hang out on the ice, to begin with? Simple. In the water, seals are, themselves, potential dinners for larger creatures. On land, they have no natural predators at all and can safely bask in the sun, lying on their cute and chubby bellies for so long that their body heat hollows out divots in the ice.