One of the more common (yet bizarre and cool) snakes in Costa Rica, the Brown Blunt-headed Vine Snake (Imantodes cenchoa). These guys are super thin (their heads are 3x the width of their body) and super long. They eat small lizards and frogs.
edited 3/20/09- cropped the picture slightly to remove some distracting elements from the top.
You can also see this deviation at the group ~DeviantHerps
. Check out the page sometime.