You are truly adept with a knife in combat.
Prerequisite: Base Attack Bonus +2, Simple Weapons Proficiency, Weapon Focus (Knife)
Benefit: You treat the damage you deal with a knife as if it were one size category larger (i.e., 1d4 to 1d6)
You know how to hit where it hurts when using a knife.
Prerequisite: Base Attack Bonus +4, Knife Fighting, Simple Weapons Proficiency, Weapon Focus (knife).
Benefit: You deal an additional +2 to damage when using a knife in combat.