"Language of Man pronounced
By tongue of brute, and human sense expressed?
The first at least of these I thought denied
To beasts whom God on their creation-day
Created mute to all articulate sound" (9.553-7)
"Articulate sound" is a distinguishing feature of humans, God, and angels; Eve is curious for a moment but then (fatally) forgets about this incredibly strange disruption of God's hierarchies. As part of their punishment in Book 10, Satan (and his angels) will be temporarily deprived of the ability to use "articulate sound" (they will become figuratively "mute"), partly because of his misuse of that gift here.