Telling Blow

(Player's Handbook II, page 83, DnD 3.5)

[General]

When you strike an opponent's vital areas, you draw on your ability to land crippling blows to make the most of your attack.

Prerequisite

Skirmish or sneak attack ability

Benefit

When you score a critical hit against a target, you deal your skirmish or sneak attack damage in addition to the damage from your critical hit. Your critical multiplier applies only to your normal damage, not your skirmish or sneak attack damage. This benefit affects both melee and ranged attacks.