Disemboweling Strike

 
Prerequisite(s): Sneak Attack +5d6, Weapon Focus (Any Slashing weapon)
 
Benefit: Your successful sneak attack with a slashing weapon that you have weapon focus with, deals 1d4 points of Con 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.
 
Source: Complete Scoundrel