The arrow - Hebrew “the son of the bow.” So Lamentations 3:13, margin. This use of the word son is common in the Scriptures and in all Oriental poetry.
Sling-stones - The sling was early used in war and in hunting, and by skill and practice it could be so employed as to be a formidable weapon; see Judges 20:16; 1Sa 17:40, 1 Samuel 17:49. As one of the weapons of attack on a foe it is mentioned here, though there is no evidence that the sling was ever actually used in endeavoring to destroy the crocodile. The meaning is, that all the common weapons used by men in attacking an enemy had no effect on him.
Are turned with him into stubble - Produce no more effect on him than it would to throw stubble at him.