Your poison attack is more effective.
Prerequisite: Poison attack as an extraordinary ability.
Benefit: Add +2 to the DC for Fortitude saving throws against your poison attack.
Special: The benefit of this feat stacks with the benefit provided by the Ability Focus (poison) feat.
Source: Savage Species, page 40. Added the Special section when it was seen that the Irresistible Gaze feat did the same thing with Ability Focus, justifying an otherwise useless feat in the same manner.