Break their teeth, O God, in their mouth. Serpent charmers sometimes, when they have caught their snake, proceed to beat out the poison fangs with a stone or stick. The psalmist, in the first clause, seems to allude to this practice; in the second, he changes the metaphor, reverting to his favourite image of the young lion (kephir).
Break out the great teeth of the young lions, O Lord. The "cheek teeth" (Joel 1:6), or principal fangs on either side, are intended.