Immune: constructs, kami, ooze, plant, qlippoth, undead, vermin; paladins of 3rd level or higher

A shaken character takes a –2 penalty on attack rolls, saving throws, skill checks, and ability checks. Shaken is a less severe state of fear than frightened or panicked.

Marius, Scholai Armsmaster Says: Any character can attempt to make an enemy shaken with an Intimidate check (DC 10 + HD + Wisdom modifier + situational saving throws against fear). Since shaken causes a -2 penalty to saving throws, intimidating warriors can set their spellcasters up for success by breaking their enemy’s resolve before the magic starts flying. If a shaken character gains the shakened condition again, they will become frightened and run away.