Gnash◆Requirements The beheaded's previous action was a jaws Strike that dealt damage to its target.
Effect The severed head makes a second jaws Strike as it violently shakes itself, trying to rip away a mouthful of flesh. On a success, the target takes an additional 1d4 slashing damage and 1 persistent bleed damage.
Source: Pathfinder Monster Core 2
Running this fight? Add the severed head to the initiative tracker: type its name and the AC, hit points and Perception for initiative fill in, and the book button shows this stat block mid-fight.