Their poison - Their malignity; their bad spirit; that which they utter or throw out of their mouth. The reference here is to what they speak or utter Psalms 58:3, and the idea is, that it is penetrating and deadly.
Like the poison of a serpent - Margin, as in Hebrew, “according to the likeness.” In this expression no particular class of serpents is referred to except those which are “poisonous.”
Like the deaf adder - Margin, “asp.” The word may refer either to the viper, the asp, or the adder. See the notes at Isaiah 11:8. The “particular” idea here is, that the serpent referred to was as it were “deaf;” it could not be tamed or charmed; it seemed to stop its own ears, so that there was no means of rendering it a safe thing to approach it. The supposition is that there “were” serpents which, though deadly in their poison, “might” be charmed or tamed, but that “this” species of serpent could “not.” The sense, as applied to the wicked, is, that there was no way of overcoming their evil propensities - of preventing them from giving utterance to words that were like poison, or from doing mischief to all with whom they came in contact. They were malignant, and there was no power of checking their malignity. Their poison was deadly, and there was no possibility of restraining them from doing evil.
That stoppeth her ear - Which “seems” to stop her ear; which refuses to hear the words and incantations by which other serpents are subdued and tamed. Others, however, refer this to the man himself, meaning, “like the deaf adder he stops his ear;” that is, he voluntarily makes himself like the adder that does not hear, and that will not be tamed. The former interpretation, however, is to be preferred.