| Paladin of Baha-who? |
Should be in rules forum. It depends on whether the creature is using a natural weapon that is not associated with the limbs it is using to fire the crossbow, or whether it removed one of its hands from the crossbow as a free action after firing before the end of its turn. If the answer to either of these is yes, then it can take an AoO with that natural weapon out of its turn.