By comparing himself to a worm, David was expressing his feelings of worthlessness, vulnerability, and contempt in the eyes of his enemies. The figure pictures feeling less than human (cf. Job 25:6; Isaiah 41:14). These foes were insulting him, despising him, and mocking his faith in God because the Lord was not rescuing him (cf. Matthew 27:39; Matthew 27:44). Shaking the head can signify rejection (cf. Psalm 109:25) or astonishment (cf. Psalm 64:8 : Lamentations 2:15). The Lord Jesus" enemies spoke these very words as He hung on the cross ( Matthew 27:42-43). [source][source][source]