Darts are counted as stubble
Darts being mentioned before, perhaps something else is meant here, and, according to Ben Gersom, the word signifies an engine out of which stones are cast to batter down walls; but these are of no avail against the leviathan;
he laugheth at the shaking of a spear;
at him, knowing it cannot hurt him; the crocodile, as Thevenot says F7, is proof against the halberd. The Septuagint version is, "the shaking of the pyrophorus", or torch bearer; one that carried a torch before the army, who, when shook, it was a token to begin the battle; which the leviathan being fearless of laughs at it; (See Gill on Obadiah 1:18).
F7 Travels, part 1. b. 2. c. 72. p. 245.