what the snow hides shall never be found
From your high vantage point, you think you catch a glimpse of something beneath the ice. It's probably a trick of the light; the sun moving out briefly from behind a cloud and making it seem as though the shadows were moving.
Surely it's just that, and nothing more. What you thought you saw was far too big to be real, of course.
Surely it's just that, and nothing more. What you thought you saw was far too big to be real, of course.