Heb harak, meaning "to grate the teeth", (Job 16:9; Ps 112:10; La 2:16), denotes rage or sorrow. (See also Ac 7:54; Mr 9:18.)
And wheresoever he taketh him, he teareth him, and he foameth and gnasheth with his teeth and pineth away. And I spake to thy disciples to cast him out, and they could not.
And hearing these things, they were cut to the heart, and gnashed their teeth upon him.