This is a brown vine snake in Costa Rica. I have seen a fair number of snakes in my days, but this was an interesting encounter. We were hiking through the forest surrounding an animal sanctuary. I had seen something move in creek ahead of us. Beth was following behind me, as I rapidly moved to the creek. She called to me saying, "Did you see this". I turned around and saw saw thin vine moving through the undergrowth. Then, I saw the vine's head. It was the first brown vine snake I had seen in the wild.
Of course, I had the wrong lens on my camera. I took a few shots because I was sure that the snake would rapidly slide off before I could change to my telephoto lens. I, then, went to change lens and a funny thing happened. The snake seemed to wait. It sat there as I changed lens, I took a few photos of its profile, and it then, almost as if on cue, it faced me. After a few more pictures, it was done, so was I, and it slipped off further into the forest.