I would agree that there are some Christians whose belief set could be vulnerable on the point of talking snakes. I can think of several different arguments depending on what other ideas they were holding in conjunction with their interpretation of Genesis. Using a blanket dismissal would have the advantage that you wouldn’t have to figure out which one would work on your target. But I think we would both agree it could also potentially backfire.

Concerning the issue you presented, that ”natural” snakes just can’t work like that. I think you have considerably underplayed your hand. Consider Gen 1:29-30:

Then God said, “Behold, I have given you every plant yielding seed that is on the surface of all the earth, and every tree which has fruit yielding seed; it shall be food for you; and to every beast of the earth and to every bird of the sky and to every thing that moves on the earth which has life, I have given every green plant for food”; and it was so.

That’s right, in the Garden of Eden every single animal was vegan. And ecosystems just don’t work like that. And I would go further and say that all these animals had the capacity at this time to live forever. Death didn’t enter the world till the fall. Rom. 5:12-14:

Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men, because all sinned— for until the Law sin was in the world, but sin is not imputed when there is no law. Nevertheless death reigned from Adam until Moses, even over those who had not sinned in the likeness of the offense of Adam, who is a type of Him who was to come.

So we are dealing with quite a big discrepancy from known biology here, and that would be a problem if I were a (Uniformitarian.)[https://en.wikipedia.org/wiki/Uniformitarianism] But fundamentalists tend to be much less Uniformitarian than main stream society. So the idea that God had a different biological system set up initially, and He changed the rules as part of the curse, seems not only plausible, but a nature part of the story.

Also it sort of seems you might be unconsciously assuming the traditional pictorial representation of a small to medium snake wrapped around a tree branch. But the text doesn't say the serpent was in the tree or give any other reference to size. I tend to picture something more like a Chinese dragon standing on all fours, shoulder to shoulder with Eve. So I don’t get the “brain box obviously too small for speech” effect from my mental picture.

(Note on the preferences for Satan controlling the snake showing an awareness that the talking snake is silly, I think this is more about emphasizing Gen. 3:15 as a Christological prophesy and generally framing the whole story as part of a Christological arch where the first Adam brings san and death and the second Adam (Jesus) brings salvation and life. Having the Devil tempting Adam and Eve here makes a parallel with Christ’s temptation in the desert and with Judas Iscariot’s temptation to betray Jesus. Finding Christological interpretations is a big motivator of Christian Theology.)