What does it mean that the frost skin is forty and the black color is two thousand feet?

It’s a snake, because the misty face comes from the poem: The frosty skin slides down the rain for forty feet, and the dark color towers two thousand feet into the sky. The original meaning of the poem is to say that a tree has a white bark and smooth trunk. Forty meters in circumference, the green-black tower reaches two thousand feet into the sky.... It is very slender. If you want to say slender, it would be a snake~~~~