But in addition to the serpent speaking to Eve, the possibility has been suggested that the serpent also ate of the fruit itself and showed that nothing immediately happened to it when that action was taken. This action (if it happened) may have proved to have been more powerful than any spoken words.
There is nothing to suggest that the literal serpent had vocal cords. But in another similar example, when God's angel spoke to Balaam through a she-ass, the animal did not need a complex voice box similar to that of a human. (Numbers 22:26-31) The power for this action came from the spirit realm. Reasonably then, the voice of the serpent must have come from some invisible person, who was using this snake as a ventriloquist uses a dummy. Possibly this was in order so Eve would not suspect that the inquirer was really an unseen spirit person that was determined to mislead her into breaking God's command and thus sinning. The spirit creature behind the serpent that spoke to Eve is identified in the Bible as "the original serpent, the one called Devil and Satan." (Revelation 12:9)
Was Satan around at the time of Adam and Eve and was he responsible for the snake? (Search For Bible Truths)
Who was the Serpent in Genesis 3? (Jehovah's Witnesses United)
Satan the Devil - Links to Information (Search For Bible Truths)
Adam and Eve - Links to Information (Defend Jehovah's Witnesses)