Charles H. Spurgeon on Psalms 140:3

Adder. The word acshub (pronounced, ak-shoob), only occurs in this one passage. The precise species represented by this word is unknown. Buxtorf, however, explains the word as the Spitter, "illud genus quod venelmm proeul exspuit." Now, if we accept this derivation, we must take the word acshub as a synonym for pethen. We have already identified the Pethen with the Naja haje, a snake which has the power of expelling the poison to some distance, when it is out of reach of its enemy. Whether the snake really intends to eject the poison, or whether it is merely flung from the hollow fangs by the force of the suddenly checked stroke, is uncertain. That the Haje cobra can expel its poison is an acknowledged fact, and the Dutch colonists of the Cape have been so familiarly acquainted with this habit, that they have called this reptile by the name of Spuugh Slange, or Spitting Snake, a name which, if we accept Buxtorf's etymology, is precisely equivalent to the word acshub. —J.G. Wood, in "Bible Animals."

Verses 3, 5, 8. Selah. We meet with Selah here for the first time since Psalm 89. From Psalm 90 to Psalm 140 no Selah occurs. Why omitted in these fifty we cannot tell any more than why so often recurring in others. However, there are only about forty Psalms in all in which it is used. —Andrew A. Bonar.