I kept missing the penguins on this walk around the sea ice on Antarctica! I would come around a wall of ice to see these trails here and there. I'm no biologist, but I did identify them as penguin-belly-slide-trails, I think! You can see the rut left by their belly and where the little flippers would steer them this way and that.
I did get to see a lot of penguins sliding around, but never quite this close… maybe next time!