The Serpent’s extreme intelligence and ability to speak can really only be explained by it being human. The Lilith legend provides the only plausible origin for this human.
Could the Serpent have been an ordinary animal that was somehow supernaturally given the power of speech? The evidence says no. The literal Hebrew of Ge 3:1 states that the Serpent itself is intelligent and crafty among all the mammals. It is not an indwelling demonic spirit that imparts the Serpent with these abilities. Intelligence and craftiness are innate in the creature. Indeed, the general tenor of Genesis implies that the Serpent’s intelligence and ability to speak is not supernatural or unexpected, but rather the natural created state of the being. It certainly did not surprise Adam or Eve to see the Serpent talking. Eve held a long discussion with the Serpent and was deceived by it. It is inconceivable that she would express no surprise or inquire over seeing an animal speaking.
There is only one instance in the Bible of an animal speaking through some type of supernatural intervention, and in that case, the feat was meant to astonish the witnesses. The event comes in Nu 22:28-30. There Jehovah opens the mouth of Balaam’s ass to rebuke its rider. Jehovah is using the ass to demonstrate the spiritual blindness which had come over Balaam, whose ways had become perverse to God. The ass was able to see an armed angel blocking the way, but Balaam was not. God supernaturally gave the ass speech as a rebuke to Balaam. The absurdity of a talking ass wiser than its rider was meant to impress upon Balaam how perverse he had become. While it is certainly conceivable that the Lucifer could manifest similar power and cause the Serpent to speak, Adam and Eve’s shock at the site should have certainly matched Balaam’s. Neither Eve nor Adam expressed any astonishment at seeing the Serpent speak. The Serpent must have been human.