ירמיהו, פרק ח׳, פסוק י״ז

A terrifying image of venomous, unstoppable reptiles illustrates the cruel nature of an approaching enemy and the complete helplessness of the people. God declares that He is actively inciting and provoking these creatures against them [מצודת ציון]. They are a family of deadly, evil serpents [מצודת ציון, ביאור שטיינזלץ], specifically described as vipers [מלבי״ם]. The primary approach among commentators is that these snakes are a metaphor for murderous nations that God is bringing against Israel [רד״ק]. This enemy will not act with any humanity, but will instead attack with animalistic cruelty [אברבנאל].

The unique danger of these serpents is that they cannot be charmed. On a literal level, no magic spell can prevent their arrival or heal their bite [ביאור שטיינזלץ]. A Midrashic tradition explains that when a snake reaches seventy years of age, it becomes a viper and deliberately plugs its ears so it will not hear the soothing voice of a charmer [רש״י].

Symbolically, this inability to charm the snakes represents the complete uselessness of trying to appease the enemy. Just as the viper is deaf to charms, the invaders will be deaf to pleas. They cannot be pacified with soft words or cries for mercy [מצודת דוד, אברבנאל]. The unavoidable result is a fatal strike, as the enemies will attack and kill without any pity [רד״ק, מצודת ציון].