Vicious

Vicious weapons have sinister appearances. A vicious weapon gains the boost special weapon property, but when you make an attack with the boosted damage, you take damage equal to the additional boost damage. This damage applies even if your attack misses, and it is not reduced by DR, resistance, or any other ability. The boost is 1d4, plus an additional 1d4 for every 6 item levels the weapon has. If the weapon does not use charges or ammunition, boosting it takes a standard action and does not expend any additional charges or ammunition. You cannot boost an attack made with the automatic, blast, explode, or line weapon special property. Weapons that have the boost special weapon property cannot be vicious.