+1 Sai of Snaring

If a monk attacks with this weapon and slides a natural 20, the victim of the attack will drop a blade weapon. If the victim of the attack is wielding a non-blade weapon (e.g., hammer), it will not be disarmed. Natural weapons (e.g., claws) cannot be disarmed. The natural 20 attack will still hit and almost certainly cause damage, but it won’t disarm the monster.

The disarm effect of this weapon is triggered by sliding a natural 20. It does not require a critical hit. Thus it will still function when fighting undead, constructs, or any creature which is immune to critical hits—as long as the victim is wielding a bladed weapon.