When a character is strangled by an instrument or an attacker, use the rules below.
A character can strangle or choke a target of the same size category or one size category larger or smaller. The strangling attempt incurs an attack of opportunity.
To begin the choke, the attacker must succeed at an opposed grapple check. If the grapple succeeds, the attacker can choose to deal normal unarmed damage as well as choke the target. The target can hold his of her breath for a number of rounds equal to his or her Constitution score. After this period of time, the target must make a Constitution check (DC 10, +1 for each previous check) every round to continue holding his or her breath. The target begins to suffocate on a failed check (see Suffocation and Drowning).
If at any time the target breaks free or slips free of the grapple, the stranglehold is broken (although any damage that was dealt remains). Note that a grappled target who is not pinned can use his or her attack action to strangle his or her attacker.