Disemboweling Strike( Complete Scoundrel, p. 0)
You can slash open your opponent to devastating effect.
Weapon Focus (PH) (Any slashing weapon) , Sneak attack +5d6,
Your successful sneak attack with a slashing weapon for which you have selected Weapon Focus deals 1d4 points of Constitution damage in addition to its normal damage. You can't use this feat against the same target more than once per day. Using this feat reduces your sneak attack damage by 4d6.