Embodiments of the Expandable Arrow Nock are comprised of a nock tip, expandable fins, an internal spring, a high tensile strength wire and a pass-through module. When the arrow is fired, the fins are in the stowed position and remain in the stowed position as the arrow travels up to the point where the arrow hits the target animal. At the point where the arrow hits the target animal, the deceleration of the arrow at that instant actuates the compressed internal spring that in turn force the fins into the deployed or open position. The deployed fins prevent the nock from travelling through the body of the animal. However, the shaft portion of the arrow detaches from the nock and pass-through module.