Grapple: Chokehold

You attempt to choke a creature you are grappling until it is unconscious. You may replace an attack action with a special grapple attack against a creature grappled by you. On a success, the grappled creature takes nonlethal bludgeoning damage equal to the maximum roll of one of its hit die at the start of each of your turns.

The DM informs you of the creatures HD size if necessary.