While transformed into the shape of a wild animal, you can savagely tear at any creature that you manage to grapple.
Prerequisites: Wild shape, sneak attack +1d6.
Benefit: While you are in a wild shape, any time you make a successful grapple check to damage a creature with which you are already grappling, you can add your sneak attack damage as well. Creatures not subject to sneak attacks don’t take this extra damage.
Source: Complete Adventurer, page 114.