You have a greater chance to resist attacks against your willpower, but at a cost.
Prerequisite: Iron Will.
Benefit: Before rolling a Will save, you can decide to activate this feat, which gives you a +6 bonus on your saving throw. After the saving throw is resolved, regardless of the result, you are shaken until the end of the encounter.
Source: Savage Species, page 31. Removed last sentence and hyperlinked the shaken condition to the version 3.5 definition.