This is one of three (maybe soon to be four) Hypnale species in Sri Lanka, all of which look quite similar. It seems that this group of vipers didn't want the Sri Lankan agamid lizards to get all the attention for their silly snouts. This one is an adult, posed on a rock, maybe 18 inches long.

A couple of nights later I spotted another in the very rainy rainforest. This one is a little baby, in coiled-up form no more than a couple of inches in diameter.