Two-Weapon Rend
Striking with both of your weapons simultaneously, you can use them to deliver devastating wounds.
Prerequisite: Dex 17, Double Slice, Improved Two-Weapon Fighting, Two-Weapon Fighting, base attack bonus +11.
Benefit: If you hit an opponent with both your primary hand and your off-hand weapon, you deal an additional 1d10 points of damage plus 1-1/2 times your Strength modifier. You can only deal this additional damage once each round.
Source: Pathfinder Core Rulebook, p. 136