It looked like a regular sword attack, but they also hiss with their mouths open, which is understood as drinking blood, plus they wanted to emphasize that when blood touches a dead vampire, it will revive.
Vampires with swords in Heroes 5 look great; it would be nice if a sword attack was just a sword attack, and a bite was an ability (approached, bit:smile24:), with more damage from the sword and the bite being a way to recover:smile08:.
