Maul (Special Ability)
From D&D Wiki
A creature with this special attack gains extra natural attacks when it grapples its foe. Normally, a monster can attack with only one of its natural weapons while grappling, but a monster with the maul ability usually gains an additional bite attack that it can use only against a grappled foe. Maul attacks are not subject to the usual -4 penalty for attacking with a natural weapon in a grapple.