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 wherever it seizes him it convulses him, and he foams at the mouth and grinds his teeth; and he is wasting away. I told your disciples to drive it out, and they could not do it."
When they heard that, they were enraged and ground their teeth at him.