I would like to ask this person what they mean by “Biblical Literalism”. This is such a loaded term and can mean so much to so many. But given the context of his three words, I will be assuming the view that the events described in the Bible as actual events are to be taken literally.
The first issue is that this is a straw man argument as there is an implied suggestion that Christianity is promoting the idea that snakes speak as a matter of natural occurrence. I’ve never known any Christians who are promoting this idea and the event itself is a supernatural one which is not present in normal, natural conditions.
However, this passage from Genesis 3 depicts Satan as taking the form of a serpent and deceiving Eve. Satan has been described in many ways throughout the Bible including as being a dragon. But Christians are not suggesting that dragons are real any more than suggesting that unicorns are real. But it isn't just a talking snake in Genesis, there is another recorded instance in the Bible where an animal speaks.
The story of Balaam’s donkey is an event in Numbers where God sends an angel to stop Balaam on his way to curse the nation of Israel on the behalf of the Moabites.
“But God was incensed that Balaam was going, and the Angel of the Lord took His stand on the path to oppose him. Balaam was riding his donkey, and his two servants were with him. When the donkey saw the Angel of the Lord standing on the path with a drawn sword in His hand, she turned off the path and went into the field. So, Balaam hit her to return her to the path. Then the Angel of the Lord stood in a narrow passage between the vineyards, with a stone wall on either side. The donkey saw the Angel of the Lord and pressed herself against the wall, squeezing Balaam’s foot against it. So he hit her once again. The Angel of the Lord went ahead and stood in a narrow place where there was no room to turn to the right or the left. When the donkey saw the Angel of the Lord, she crouched down under Balaam. So he became furious and beat the donkey with his stick.
Then the Lord opened the donkey’s mouth, and she asked Balaam, “What have I done to you that you have beaten me these three times?” Numbers 22:21-39 HCSB
It is clear from this passage that a speaking donkey is not a normal, natural occurrence and would be considered a miracle. God caused the donkey to be able to speak. This does not mean that the Bible or Christianity is suggesting that donkeys can talk.
This brings us to problem number two which is the main undergirding of the objection. Most skeptics will assert that the supernatural is not possible and that an appeal as such is not falsifiable. Falsifiability, however, is related to a scientific inquiry. The supernatural, by definition, is not something testable by science as science deals with the natural world. You can use science to falsify a specific supernatural claim (for example, a person claims to be healed from cancer, but medical records show they were never diagnosed with cancer, etc.), but science cannot show the supernatural to be false in principle. So, other tools must be used. Some skeptics argue for methodological naturalism stating that science is barred from investigating the supernatural. But this is not the case. Science can study the effects of the supernatural on the natural world. With enough effects, one could make a rational inference as to the cause and if, given the evidence, it is more reasonable for the cause to be supernatural, then such a claim could be made even if the everyday experience of the average person does not include supernatural occurrences.
Given these reasons, the three-word argument “Snakes Don’t Talk” fails to ‘debunk’ Biblical Literalism in a broad sense and more over fails to show that the supernatural is a less reasonable explanation for the events described in the biblical narratives.