Trying out a new technique today as I'm always stumped on what to do with backgrounds. This effect was achieved by spray-fixing the pencil crayon image of the snake, coating it in a layer of dark green gouache, and then lifting the dried gouache paint off with wet paper towels. It does give this great, organic texture, but I found that it obliterated a lot of the detail I had originally put in the snake. I'll have to keep playing around with that.
But tres slithery, non?
Update: Here's the same image, but I added some ink shadows around the snake to try to push it off the background. (And not taken through photoshop, like the first image).