3e SRD:Bluff Skill
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A Bluff check is opposed by the target's Sense Motive check. Favorable and unfavorable circumstances weigh heavily on the outcome of a bluff. Two circumstances can weigh against the character: The bluff is hard to believe, or the action that the target is to take goes against the target's self-interest, nature, personality, orders, etc. If it's important, the DM can distinguish between a bluff that fails because the target doesn't believe it and one that fails because it just asks too much of the target. For instance, if the target gets a +10 bonus because the bluff demands something risky of the target, and the Sense Motive check succeeds by 10 or less, then the target didn't so much see through the bluff as prove reluctant to go along with it. If the target succeeds by 11 or more, he has seen through the bluff (and would have done so even if it had not entailed any demand on him).
A successful Bluff check indicates that the target reacts as the character wishes, at least for a short time (usually 1 round or less) or believes something that the character wants him to believe.
A bluff requires interaction between the character and the target. Creatures unaware of the character cannot be bluffed. A bluff always takes at least 1 round (and is at least a full-round action) but can take much longer if the character tries something elaborate.
Feinting in Combat
The character can also use Bluff to mislead an opponent in combat so that he can't dodge the character's attack effectively. Doing so is a miscellaneous standard action that does not draw an attack of opportunity. If the character is successful, the next attack the character makes against the target does not allow him to use his Dexterity bonus to Armor Class (if any). This attack must be made on or before your next turn. Feinting in this way against a nonhumanoid is difficult because it's harder to read a strange creature's body language; the character suffers a –4 penalty. Against a creature of animal Intelligence (1 or 2) it's even harder; the character suffers a –8 penalty. Against a nonintelligent creature, it's impossible.
Creating a Diversion to Hide
The character can use Bluff to help the character hide. A successful Bluff check can give the character the momentary diversion the character needs to attempt a Hide check while people are aware of the character.
Generally, a failed Bluff check makes the target too suspicious for a bluffer to try another one in the same circumstances. For feinting in combat, the character may retry freely.
Having 5 or more ranks in Bluff gives the character a +2 synergy bonus on Intimidate and Pick Pocket checks and a +2 synergy bonus on an Innuendo check to transmit a message. Also, if the character has 5 or more ranks of Bluff, the character gets a +2 synergy bonus on Disguise checks when the character knows that the character is being observed and the character tries to act in character.