"Because it was normal"
And as you lot say that the Bible is literal - and it MUST be literal throughout; word-for-word, letter-for-letter, cover-to-cover, or by definition it's ALL lies, cover-to-cover - if a reptile with human speech abilities existed then (and nope: I'm not seeing any mention whatsoever of such becoming extinct, post-'Fall'), these amazing talking snakes must exist to this day, must they not; as your literal Bible says...!
...oh, and that was in the Old Testament. Jesus conversed with a talking donkey in the New Testament, way after the so-called 'Fall'.
So Jesus must have been either Rex Harrison or Eddie Murphy, then. [/"Dr. Dolittle"] Or the Bible is exactly like the cartoon series "My Littlest Petshop", amirite?! Strange then, how the Bible didn't specifically mention he having an ability to understand animals (PROTIP: If it isn't specifically mentioned in the literal Bible, it NEVER happened). Or that - like the talking snake malarkey in the OT - is nothing more than a LIE, ergo the entire Bible is FICTION, and "My Little Pony: Friendship is Magic" is a documentary, as it features Spike, a talking & intelligent dragon.
...but hey, one fiction's just as good as another, amirite?! [/hyper-sarcasm] [/"Dragonslayer", "Dragonheart", "Game of Thrones"...]