וְשִֽׁעֲשַׁ֥ע יוֹנֵ֖ק עַל־חֻ֣ר פָּ֑תֶן וְעַל֙ מְאוּרַ֣ת צִפְעוֹנִ֔י גָּמ֖וּל יָד֥וֹ הָדָֽה׃
Der Säugling wird spielen auf dem Loche der Natter, in die Höhle des Basilisken wird das kaum entwöhnte Kind seine Hand strecken.
Ibn Ezra on Isaiah
ושעשע And shall play. In this sense the word has always the reduplication.
Rashi on Isaiah
over the hole of an old snake over a hole in the ground in which the snake makes its nest [krot in O.F.], a cave. an old snake פֶּתֶן. A snake, when it ages, becomes deaf and is called פֶּתֶן. From then on, it cannot be charmed; as it is said (Psalms 58:6): “Who will not hearken to the voice of charmers.”