http://www.supernaturalwiki.com/index.php?title=Monsters

Vetala
Vetalas are serpent-like vampiric creatures that, like most monsters has adapted to appear human. Vetalas prefer to hunt in pairs, where they will sedate their victim(s) with venom and feed off of their blood over a number of days, with the victim typically dying after the fourth feeding. While feeding they will reveal snake-like eyes and four pointed fangs.
A vetala can be killed by stabbing it in the heart with a silver knife and then twisting, whereupon they will revert to their true serpent form in death.

[img]http://i.imgur.com/Nkj3KYF.jpg[/img]