From Pathfinder Howl of the Wild, which isn't enabled.

Sinking Jaws

FEAT 10

Prerequisites Beastmaster Dedication; animal companion with a jaws or fangs unarmed attack

Like how a constrictor wraps itself around its next meal, your companion tightens its teeth around its constrained prey to squeeze the life out of it. Your companions with a qualifying unarmed attack learn the Sinking Jaws activity.

Sinking Jaws

Requirements This companion has a creature Grabbed or Restrained with its jaws or fangs

Effect This companion's grabbed or restrained foe takes piercing damage equal to the companion's level plus Strength modifier.

Pathfinder Howl of the WildORC