Once again, my claim to offer 'exhibition quality' images is shown to be optimistic. Click to embiggen.
So we have a snake, maybe a meter long, light brown with dark brown markings. Or dark brown with light brown markings.
It scared me because I didn't see it until it was under mine and my dog's feet. It slithered away quickly and my camera focused mostly on the grass around and above the snake.
Here is what it could be:
A non-venomous rat snake that comes in many colour morphs. Wikipedia. Here is a stock image that has similar coloration. I found it here and shrank it considerably.
Or a very venomous viper. Found here, number 3 on the list. Again, highly shrunk, follow the link for full size. I think their image is of (details found here)
|Gloydius saxatilis 
|In the higher reaches of the Taebaek and Sobaek Mountains.
Of the two, the head better matches a non-venomous snake. Vipers all have diamond heads and the snake in my images and the rat snake image have a head no wider than the neck of the snake.
To do better, I need to count the scales encircling the snake and examine more closely the neck. Even if the snake were not venomous, I am loath to bother it further than I already do, chasing it with my camera out, trying to get some satisfactory image.