The material below is Open Game Content from a 3PP Source
Animal Fury (Ex): While raging, the barbarian gains a bite attack. If used as part of a full attack action, the bite attack is made at the barbarian's full base attack bonus –5. If the bite hits, it deals 1d4 points of damage (assuming the barbarian is Medium; 1d3 points of damage if Small) plus half the barbarian's Strength modifier. A barbarian can make a bite attack as part of the action to maintain or break free from a grapple. This attack is resolved before the grapple check is made. If the bite attack hits, any grapple checks made by the barbarian against the target this round are at a +2 bonus.